1
|
Beaven AH, Bikkumalla V, Chon NL, Matthews AE, Lin H, Knight JD, Sodt AJ. Synaptotagmin 7 C2 domains induce membrane curvature stress via electrostatic interactions and the wedge mechanism. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.10.575084. [PMID: 38313280 PMCID: PMC10837831 DOI: 10.1101/2024.01.10.575084] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/06/2024]
Abstract
Synaptotagmin 7 (Syt-7) is part of the synaptotagmin protein family that regulates exocytotic lipid membrane fusion. Among the family, Syt-7 stands out by its membrane binding strength and stabilization of long-lived membrane fusion pores. Given that Syt-7 vesicles form long-lived fusion pores, we hypothesize that its interactions with the membrane stabilize the specific curvatures, thicknesses, and lipid compositions that support a metastable fusion pore. Using all-atom molecular dynamics simulations and FRET-based assays of Syt-7's membrane-binding C2 domains (C2A and C2B), we found that Syt-7 C2 domains sequester anionic lipids, are sensitive to cholesterol, thin membranes, and generate lipid membrane curvature by two competing, but related mechanisms. First, Syt-7 forms strong electrostatic contacts with the membrane, generating negative curvature stress. Second, Syt-7's calcium binding loops embed in the membrane surface, acting as a wedge to thin the membrane and induce positive curvature stress. These curvature mechanisms are linked by the protein insertion depth as well as the resulting protein tilt. Simplified quantitative models of the curvature-generating mechanisms link simulation observables to their membrane-reshaping effectiveness.
Collapse
Affiliation(s)
- Andrew H. Beaven
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD
- Postdoctoral Research Associate Program, National Institute of General Medical Sciences, National Institutes of Health, Bethesda, MD
| | | | - Nara L. Chon
- Department of Chemistry, University of Colorado Denver, Denver, CO
| | | | - Hai Lin
- Department of Chemistry, University of Colorado Denver, Denver, CO
| | | | - Alexander J. Sodt
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD
| |
Collapse
|
2
|
Chon NL, Tran S, Miller CS, Lin H, Knight JD. A conserved electrostatic membrane-binding surface in synaptotagmin-like proteins revealed using molecular phylogenetic analysis and homology modeling. Protein Sci 2024; 33:e4850. [PMID: 38038838 PMCID: PMC10731544 DOI: 10.1002/pro.4850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Revised: 10/29/2023] [Accepted: 11/28/2023] [Indexed: 12/02/2023]
Abstract
Protein structure prediction has emerged as a core technology for understanding biomolecules and their interactions. Here, we combine homology-based structure prediction with molecular phylogenetic analysis to study the evolution of electrostatic membrane binding among the vertebrate synaptotagmin-like protein (Slp) family. Slp family proteins play key roles in the membrane trafficking of large dense-core secretory vesicles. Our previous experimental and computational study found that the C2A domain of Slp-4 (also called granuphilin) binds with high affinity to anionic phospholipids in the cytoplasmic leaflet of the plasma membrane through a large positively charged protein surface centered on a cluster of phosphoinositide-binding lysine residues. Because this surface contributes greatly to Slp-4 C2A domain membrane binding, we hypothesized that the net charge on the surface might be evolutionarily conserved. To test this hypothesis, the known C2A sequences of Slp-4 among vertebrates were organized by class (from mammalia to pisces) using molecular phylogenetic analysis. Consensus sequences for each class were then identified and used to generate homology structures, from which Poisson-Boltzmann electrostatic potentials were calculated. For comparison, homology structures and electrostatic potentials were also calculated for the five human Slp protein family members. The results demonstrate that the charge on the membrane-binding surface is highly conserved throughout the evolution of Slp-4, and more highly conserved than many individual residues among the human Slp family paralogs. Such molecular phylogenetic-driven computational analysis can help to describe the evolution of electrostatic interactions between proteins and membranes which are crucial for their function.
Collapse
Affiliation(s)
- Nara L. Chon
- Department of ChemistryUniversity of Colorado DenverDenverColoradoUSA
| | - Sherleen Tran
- Department of ChemistryUniversity of Colorado DenverDenverColoradoUSA
| | | | - Hai Lin
- Department of ChemistryUniversity of Colorado DenverDenverColoradoUSA
| | | |
Collapse
|
3
|
Chon NL, Tran S, Miller CS, Lin H, Knight JD. A Conserved Electrostatic Membrane-Binding Surface in Synaptotagmin-Like Proteins Revealed Using Molecular Phylogenetic Analysis and Homology Modeling. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.13.548768. [PMID: 37502952 PMCID: PMC10369986 DOI: 10.1101/2023.07.13.548768] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
Protein structure prediction has emerged as a core technology for understanding biomolecules and their interactions. Here, we combine homology-based structure prediction with molecular phylogenetic analysis to study the evolution of electrostatic membrane binding among vertebrate synaptotagmin-like proteins (Slps). Slp family proteins play key roles in the membrane trafficking of large dense-core secretory vesicles. Our previous experimental and computational study found that the C2A domain of Slp-4 (also called granuphilin) binds with high affinity to anionic phospholipids in the cytoplasmic leaflet of the plasma membrane through a large positively charged protein surface centered on a cluster of phosphoinositide-binding lysine residues. Because this surface contributes greatly to Slp-4 C2A domain membrane binding, we hypothesized that the net charge on the surface might be evolutionarily conserved. To test this hypothesis, the known C2A sequences of Slp-4 among vertebrates were organized by class (from mammalia to pisces) using molecular phylogenetic analysis. Consensus sequences for each class were then identified and used to generate homology structures, from which Poisson-Boltzmann electrostatic potentials were calculated. For comparison, homology structures and electrostatic potentials were also calculated for the five human Slp protein family members. The results demonstrate that the charge on the membrane-binding surface is highly conserved throughout the evolution of Slp-4, and more highly conserved than many individual residues among the human Slp family paralogs. Such molecular phylogenetic-driven computational analysis can help to describe the evolution of electrostatic interactions between proteins and membranes which are crucial for their function.
Collapse
Affiliation(s)
- Nara L. Chon
- Department of Chemistry, University of Colorado Denver
| | - Sherleen Tran
- Department of Chemistry, University of Colorado Denver
| | | | - Hai Lin
- Department of Chemistry, University of Colorado Denver
| | | |
Collapse
|
4
|
Synaptotagmin 9 Modulates Spontaneous Neurotransmitter Release in Striatal Neurons by Regulating Substance P Secretion. J Neurosci 2023; 43:1475-1491. [PMID: 36732068 PMCID: PMC9992334 DOI: 10.1523/jneurosci.1857-22.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 01/05/2023] [Accepted: 01/10/2023] [Indexed: 02/04/2023] Open
Abstract
Synaptotagmin 9 (SYT9) is a tandem C2 domain Ca2+ sensor for exocytosis in neuroendocrine cells; its function in neurons remains unclear. Here, we show that, in mixed-sex cultures, SYT9 does not trigger rapid synaptic vesicle exocytosis in mouse cortical, hippocampal, or striatal neurons, unless it is massively overexpressed. In striatal neurons, loss of SYT9 reduced the frequency of spontaneous neurotransmitter release events (minis). We delved into the underlying mechanism and discovered that SYT9 was localized to dense-core vesicles that contain substance P (SP). Loss of SYT9 impaired SP release, causing the observed decrease in mini frequency. This model is further supported by loss of function mutants. Namely, Ca2+ binding to the C2A domain of SYT9 triggered membrane fusion in vitro, and mutations that disrupted this activity abolished the ability of SYT9 to regulate both SP release and mini frequency. We conclude that SYT9 indirectly regulates synaptic transmission in striatal neurons by controlling SP release.SIGNIFICANCE STATEMENT Synaptotagmin 9 (SYT9) has been described as a Ca2+ sensor for dense-core vesicle (DCV) exocytosis in neuroendocrine cells, but its role in neurons remains unclear, despite widespread expression in the brain. This article examines the role of SYT9 in synaptic transmission across cultured cortical, hippocampal, and striatal neuronal preparations. We found that SYT9 regulates spontaneous neurotransmitter release in striatal neurons by serving as a Ca2+ sensor for the release of the neuromodulator substance P from DCVs. This demonstrates a novel role for SYT9 in neurons and uncovers a new field of study into neuromodulation by SYT9, a protein that is widely expressed in the brain.
Collapse
|
5
|
Weingarten DJ, Shrestha A, Juda-Nelson K, Kissiwaa SA, Spruston E, Jackman SL. Fast resupply of synaptic vesicles requires synaptotagmin-3. Nature 2022; 611:320-325. [PMID: 36261524 DOI: 10.1038/s41586-022-05337-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Accepted: 09/12/2022] [Indexed: 01/09/2023]
Abstract
Sustained neuronal activity demands a rapid resupply of synaptic vesicles to maintain reliable synaptic transmission. Such vesicle replenishment is accelerated by submicromolar presynaptic Ca2+ signals by an as-yet unidentified high-affinity Ca2+ sensor1,2. Here we identify synaptotagmin-3 (SYT3)3,4 as that presynaptic high-affinity Ca2+ sensor, which drives vesicle replenishment and short-term synaptic plasticity. Synapses in Syt3 knockout mice exhibited enhanced short-term depression, and recovery from depression was slower and insensitive to presynaptic residual Ca2+. During sustained neuronal firing, SYT3 accelerated vesicle replenishment and increased the size of the readily releasable pool. SYT3 also mediated short-term facilitation under conditions of low release probability and promoted synaptic enhancement together with another high-affinity synaptotagmin, SYT7 (ref. 5). Biophysical modelling predicted that SYT3 mediates both replenishment and facilitation by promoting the transition of loosely docked vesicles to tightly docked, primed states. Our results reveal a crucial role for presynaptic SYT3 in the maintenance of reliable high-frequency synaptic transmission. Moreover, multiple forms of short-term plasticity may converge on a mechanism of reversible, Ca2+-dependent vesicle docking.
Collapse
Affiliation(s)
| | - Amita Shrestha
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA
| | - Kessa Juda-Nelson
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA
| | - Sarah A Kissiwaa
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA
| | - Evan Spruston
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA
| | - Skyler L Jackman
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA.
| |
Collapse
|
6
|
Henry D, Joselevitch C, Matthews GG, Wollmuth LP. Expression and distribution of synaptotagmin family members in the zebrafish retina. J Comp Neurol 2022; 530:705-728. [PMID: 34468021 PMCID: PMC8792163 DOI: 10.1002/cne.25238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Revised: 08/21/2021] [Accepted: 08/24/2021] [Indexed: 11/10/2022]
Abstract
Synaptotagmins belong to a large family of proteins. Although various synaptotagmins have been implicated as Ca2+ sensors for vesicle replenishment and release at conventional synapses, their roles at retinal ribbon synapses remain incompletely understood. Zebrafish is a widely used experimental model for retinal research. We therefore investigated the homology between human, rat, mouse, and zebrafish synaptotagmins 1-10 using a bioinformatics approach. We also characterized the expression and distribution of various synaptotagmin (syt) genes in the zebrafish retina using RT-PCR, qPCR, and in situhybridization, focusing on the family members whose products likely underlie Ca2+ -dependent exocytosis in the central nervous system (synaptotagmins 1, 2, 5, and 7). Most zebrafish synaptotagmins are well conserved and can be grouped in the same classes as mammalian synaptotagmins, based on crucial amino acid residues needed for coordinating Ca2+ binding and determining phospholipid binding affinity. The only exception is synaptotagmin 1b, which lacks 34 amino acid residues in the C2B domain and is therefore unlikely to bind Ca2+ there. Additionally, the products of zebrafish syt5a and syt5b genes share identity with mammalian class 1 and 5 synaptotagmins. Zebrafish syt1, syt2, syt5, and syt7 paralogues are found in the zebrafish brain, eye, and retina, excepting syt1b, which is only present in the brain. The complementary expression pattern of the remaining paralogues in the retina suggests that syt1a and syt5a may underlie synchronous release and syt7a and syt7b may mediate asynchronous release or other Ca2+ -dependent processes in different retinal neurons.
Collapse
Affiliation(s)
- Diane Henry
- Department of Neurobiology & Behavior, Stony Brook University, Stony Brook, NY 11794-5230,Center for Nervous System Disorders, Stony Brook University, Stony Brook, NY 11794-5230
| | - Christina Joselevitch
- Department of Neurobiology & Behavior, Stony Brook University, Stony Brook, NY 11794-5230,Center for Nervous System Disorders, Stony Brook University, Stony Brook, NY 11794-5230
| | - Gary G. Matthews
- Department of Neurobiology & Behavior, Stony Brook University, Stony Brook, NY 11794-5230,Center for Nervous System Disorders, Stony Brook University, Stony Brook, NY 11794-5230
| | - Lonnie P. Wollmuth
- Department of Neurobiology & Behavior, Stony Brook University, Stony Brook, NY 11794-5230,Department of Biochemistry & Cell Biology, Stony Brook University, Stony Brook, NY 11794-5230,Center for Nervous System Disorders, Stony Brook University, Stony Brook, NY 11794-5230
| |
Collapse
|
7
|
Development of the hypersecretory phenotype in the population of adrenal chromaffin cells from prehypertensive SHRs. Pflugers Arch 2021; 473:1775-1793. [PMID: 34510285 DOI: 10.1007/s00424-021-02614-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 08/10/2021] [Accepted: 08/11/2021] [Indexed: 10/20/2022]
Abstract
The hypersecretory phenotype of adrenal chromaffin cells (CCs) from early spontaneously hypertensive rats (SHRs) mainly results from enhanced Ca2+-induced Ca2+-release (CICR). A key question is if these abnormalities can be traced to the prehypertensive stage. Spontaneous and stimulus-induced catecholamine exocytosis, intracellular Ca2+ signals, and dense-core granule size and density were examined in CCs from prehypertensive and hypertensive SHRs and compared with age-matched Wistar-Kyoto rats (WKY). During the prehypertensive stage, the depolarization-elicited catecholamine exocytosis was ~ 2.9-fold greater in SHR than in WKY CCs. Interestingly, in half of CCs the exocytosis was indistinguishable from WKY CCs, while it was between 3- and sixfold larger in the other half. Likewise, caffeine-induced exocytosis was ~ twofold larger in prehypertensive SHR. Accordingly, depolarization and caffeine application elicited [Ca2+]i rises ~ 1.5-fold larger in prehypertensive SHR than in WKY CCs. Ryanodine reduced the depolarization-induced secretion in prehypertensive SHR by 57%, compared to 14% in WKY CCs, suggesting a greater contribution of intracellular Ca2+ release to exocytosis. In SHR CCs, the mean spike amplitude and charge per spike were significantly larger than in WKY CCs, regardless of age and stimulus type. This difference in granule content could explain in part the enhanced exocytosis in SHR CCs. However, electron microscopy did not reveal significant differences in granule size between SHRs and WKY rats' adrenal medulla. Nonetheless, preSHR and hypSHR display 63% and 82% more granules than WKY, which could explain in part the enhanced catecholamine secretion. The mechanism responsible for the heterogeneous population of prehypertensive SHR CCs and the bias towards secreting more medium and large granules remains unexplained.
Collapse
|
8
|
Wu Z, Dharan N, McDargh ZA, Thiyagarajan S, O'Shaughnessy B, Karatekin E. The neuronal calcium sensor Synaptotagmin-1 and SNARE proteins cooperate to dilate fusion pores. eLife 2021; 10:68215. [PMID: 34190041 PMCID: PMC8294851 DOI: 10.7554/elife.68215] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Accepted: 06/29/2021] [Indexed: 02/07/2023] Open
Abstract
All membrane fusion reactions proceed through an initial fusion pore, including calcium-triggered release of neurotransmitters and hormones. Expansion of this small pore to release cargo is energetically costly and regulated by cells, but the mechanisms are poorly understood. Here, we show that the neuronal/exocytic calcium sensor Synaptotagmin-1 (Syt1) promotes expansion of fusion pores induced by SNARE proteins. Pore dilation relied on calcium-induced insertion of the tandem C2 domain hydrophobic loops of Syt1 into the membrane, previously shown to reorient the C2 domain. Mathematical modelling suggests that C2B reorientation rotates a bound SNARE complex so that it exerts force on the membranes in a mechanical lever action that increases the height of the fusion pore, provoking pore dilation to offset the bending energy penalty. We conclude that Syt1 exerts novel non-local calcium-dependent mechanical forces on fusion pores that dilate pores and assist neurotransmitter and hormone release.
Collapse
Affiliation(s)
- Zhenyong Wu
- Department of Cellular and Molecular Physiology, Yale University, New Haven, United States.,Nanobiology Institute, Yale University, West Haven, United States
| | - Nadiv Dharan
- Department of Chemical Engineering, Columbia University, New York, United States
| | - Zachary A McDargh
- Department of Chemical Engineering, Columbia University, New York, United States
| | - Sathish Thiyagarajan
- Department of Chemical Engineering, Columbia University, New York, United States
| | - Ben O'Shaughnessy
- Department of Chemical Engineering, Columbia University, New York, United States
| | - Erdem Karatekin
- Department of Cellular and Molecular Physiology, Yale University, New Haven, United States.,Nanobiology Institute, Yale University, West Haven, United States.,Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, United States.,Saints-Pères Paris Institute for the Neurosciences (SPPIN), Université de Paris, Centre National de la Recherche Scientifique (CNRS) UMR 8003, Paris, France
| |
Collapse
|
9
|
van Westen R, Poppinga J, Díez Arazola R, Toonen RF, Verhage M. Neuromodulator release in neurons requires two functionally redundant calcium sensors. Proc Natl Acad Sci U S A 2021; 118:e2012137118. [PMID: 33903230 PMCID: PMC8106342 DOI: 10.1073/pnas.2012137118] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Neuropeptides and neurotrophic factors secreted from dense core vesicles (DCVs) control many brain functions, but the calcium sensors that trigger their secretion remain unknown. Here, we show that in mouse hippocampal neurons, DCV fusion is strongly and equally reduced in synaptotagmin-1 (Syt1)- or Syt7-deficient neurons, but combined Syt1/Syt7 deficiency did not reduce fusion further. Cross-rescue, expression of Syt1 in Syt7-deficient neurons, or vice versa, completely restored fusion. Hence, both sensors are rate limiting, operating in a single pathway. Overexpression of either sensor in wild-type neurons confirmed this and increased fusion. Syt1 traveled with DCVs and was present on fusing DCVs, but Syt7 supported fusion largely from other locations. Finally, the duration of single DCV fusion events was reduced in Syt1-deficient but not Syt7-deficient neurons. In conclusion, two functionally redundant calcium sensors drive neuromodulator secretion in an expression-dependent manner. In addition, Syt1 has a unique role in regulating fusion pore duration.
Collapse
Affiliation(s)
- Rhodé van Westen
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
- Department of Clinical Genetics, Amsterdam University Medical Centers, 1081 HV Amsterdam, The Netherlands
| | - Josse Poppinga
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
| | - Rocío Díez Arazola
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
| | - Ruud F Toonen
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands;
| | - Matthijs Verhage
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands;
- Department of Clinical Genetics, Amsterdam University Medical Centers, 1081 HV Amsterdam, The Netherlands
| |
Collapse
|
10
|
Hark TJ, Rao NR, Castillon C, Basta T, Smukowski S, Bao H, Upadhyay A, Bomba-Warczak E, Nomura T, O'Toole ET, Morgan GP, Ali L, Saito T, Guillermier C, Saido TC, Steinhauser ML, Stowell MHB, Chapman ER, Contractor A, Savas JN. Pulse-Chase Proteomics of the App Knockin Mouse Models of Alzheimer's Disease Reveals that Synaptic Dysfunction Originates in Presynaptic Terminals. Cell Syst 2020; 12:141-158.e9. [PMID: 33326751 DOI: 10.1016/j.cels.2020.11.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Revised: 09/23/2020] [Accepted: 11/19/2020] [Indexed: 12/14/2022]
Abstract
Compromised protein homeostasis underlies accumulation of plaques and tangles in Alzheimer's disease (AD). To observe protein turnover at early stages of amyloid beta (Aβ) proteotoxicity, we performed pulse-chase proteomics on mouse brains in three genetic models of AD that knock in alleles of amyloid precursor protein (APP) prior to the accumulation of plaques and during disease progression. At initial stages of Aβ accumulation, the turnover of proteins associated with presynaptic terminals is selectively impaired. Presynaptic proteins with impaired turnover, particularly synaptic vesicle (SV)-associated proteins, have elevated levels, misfold in both a plaque-dependent and -independent manner, and interact with APP and Aβ. Concurrent with elevated levels of SV-associated proteins, we found an enlargement of the SV pool as well as enhancement of presynaptic potentiation. Together, our findings reveal that the presynaptic terminal is particularly vulnerable and represents a critical site for manifestation of initial AD etiology. A record of this paper's transparent peer review process is included in the Supplemental Information.
Collapse
Affiliation(s)
- Timothy J Hark
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Nalini R Rao
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Charlotte Castillon
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Tamara Basta
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, CO 80309, USA
| | - Samuel Smukowski
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Huan Bao
- Department of Neuroscience and Howard Hughes Medical Institute, University of Wisconsin, Madison, WI 53706, USA; Department of Molecular Medicine, The Scripps Research Institute, Jupiter, FL 33458, USA
| | - Arun Upadhyay
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Ewa Bomba-Warczak
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Toshihiro Nomura
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Eileen T O'Toole
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, CO 80309, USA
| | - Garry P Morgan
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, CO 80309, USA
| | - Laith Ali
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Takashi Saito
- Laboratory of Proteolytic Neuroscience, RIKEN Center for Brain Science, Wako, Saitama 351-0198, Japan; Department of Neurocognitive Science, Institute of Brain Science, Nagoya City University Graduate School of Medical Science, Nagoya, Aichi 467-8601, Japan
| | - Christelle Guillermier
- Center for NanoImaging, Brigham and Women's Hospital and Harvard Medical School, Cambridge, MA 02138, USA
| | - Takaomi C Saido
- Laboratory of Proteolytic Neuroscience, RIKEN Center for Brain Science, Wako, Saitama 351-0198, Japan
| | - Matthew L Steinhauser
- Center for NanoImaging, Brigham and Women's Hospital and Harvard Medical School, Cambridge, MA 02138, USA; Department of Medicine, Divisions of Genetics and Cardiovascular Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA
| | - Michael H B Stowell
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, CO 80309, USA; Department of Mechanical Engineering, University of Colorado at Boulder, Boulder, CO 80309, USA
| | - Edwin R Chapman
- Department of Neuroscience and Howard Hughes Medical Institute, University of Wisconsin, Madison, WI 53706, USA
| | - Anis Contractor
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA; Department of Neurobiology, Weinberg College of Arts and Sciences, Northwestern University, Chicago, IL 60611, USA
| | - Jeffrey N Savas
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
| |
Collapse
|
11
|
Wolfes AC, Dean C. The diversity of synaptotagmin isoforms. Curr Opin Neurobiol 2020; 63:198-209. [PMID: 32663762 DOI: 10.1016/j.conb.2020.04.006] [Citation(s) in RCA: 53] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2020] [Revised: 04/07/2020] [Accepted: 04/10/2020] [Indexed: 12/20/2022]
Abstract
The synaptotagmin family of molecules is known for regulating calcium-dependent membrane fusion events. Mice and humans express 17 synaptotagmin isoforms, where most studies have focused on isoforms 1, 2, and 7, which are involved in synaptic vesicle exocytosis. Recent work has highlighted how brain function relies on additional isoforms, with roles in postsynaptic receptor endocytosis, vesicle trafficking, membrane repair, synaptic plasticity, and protection against neurodegeneration, for example, in addition to the traditional concept of synaptotagmin-mediated neurotransmitter release - in neurons as well as glia, and at different timepoints. In fact, it is not uncommon for the same isoform to feature several splice isoforms, form homo- and heterodimers, and function in different subcellular locations and cell types. This review aims to highlight the diversity of synaptotagmins, offers a concise summary of key findings on all isoforms, and discusses different ways of grouping these.
Collapse
Affiliation(s)
- Anne C Wolfes
- Department of Brain Sciences, Division of Neuroscience, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London, W12 0NN, UK; UK Dementia Research Institute at Imperial College, London, UK
| | - Camin Dean
- German Center for Neurodegenerative Diseases, Charité University of Medicine - Berlin, 10117 Berlin, Germany.
| |
Collapse
|
12
|
Bartholome O, de la Brassinne Bonardeaux O, Neirinckx V, Rogister B. A Composite Sketch of Fast-Spiking Parvalbumin-Positive Neurons. Cereb Cortex Commun 2020; 1:tgaa026. [PMID: 34296100 PMCID: PMC8153048 DOI: 10.1093/texcom/tgaa026] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Revised: 06/15/2020] [Accepted: 06/15/2020] [Indexed: 01/28/2023] Open
Abstract
Parvalbumin-positive neurons are inhibitory neurons that release GABA and are mostly represented by fast-spiking basket or chandelier cells. They constitute a minor neuronal population, yet their peculiar profiles allow them to react quickly to any event in the brain under normal or pathological conditions. In this review, we will summarize the current knowledge about the fundamentals of fast-spiking parvalbumin-positive neurons, focusing on their morphology and specific channel/protein content. Next, we will explore their development, maturation, and migration in the brain. Finally, we will unravel their potential contribution to the physiopathology of epilepsy.
Collapse
Affiliation(s)
| | | | | | - Bernard Rogister
- GIGA-Neurosciences, University of Liege, 4000 Liège, Belgium.,Neurology Department, CHU, Academic Hospital, University of Liege, 4000 Liège, Belgium
| |
Collapse
|
13
|
Liang T, Qin T, Kang F, Kang Y, Xie L, Zhu D, Dolai S, Greitzer-Antes D, Baker RK, Feng D, Tuduri E, Ostenson CG, Kieffer TJ, Banks K, Pessin JE, Gaisano HY. SNAP23 depletion enables more SNAP25/calcium channel excitosome formation to increase insulin exocytosis in type 2 diabetes. JCI Insight 2020; 5:129694. [PMID: 32051343 PMCID: PMC7098801 DOI: 10.1172/jci.insight.129694] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2019] [Accepted: 01/15/2020] [Indexed: 01/05/2023] Open
Abstract
SNAP23 is the ubiquitous SNAP25 isoform that mediates secretion in non-neuronal cells, similar to SNAP25 in neurons. However, some secretory cells like pancreatic islet β cells contain an abundance of both SNAP25 and SNAP23, where SNAP23 is believed to play a redundant role to SNAP25. We show that SNAP23, when depleted in mouse β cells in vivo and human β cells (normal and type 2 diabetes [T2D] patients) in vitro, paradoxically increased biphasic glucose-stimulated insulin secretion corresponding to increased exocytosis of predocked and newcomer insulin granules. Such effects on T2D Goto-Kakizaki rats improved glucose homeostasis that was superior to conventional treatment with sulfonylurea glybenclamide. SNAP23, although fusion competent in slower secretory cells, in the context of β cells acts as a weak partial fusion agonist or inhibitory SNARE. Here, SNAP23 depletion promotes SNAP25 to bind calcium channels more quickly and longer where granule fusion occurs to increase exocytosis efficiency. β Cell SNAP23 antagonism is a strategy to treat diabetes.
Collapse
Affiliation(s)
- Tao Liang
- Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Tairan Qin
- Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Fei Kang
- Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Youhou Kang
- Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Li Xie
- Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Dan Zhu
- Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Subhankar Dolai
- Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Dafna Greitzer-Antes
- Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Robert K. Baker
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
| | - Daorong Feng
- Michael F. Price Center for Genetic and Translational Medicine, Department of Medicine and Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Eva Tuduri
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
| | - Claes-Goran Ostenson
- Department of Molecular Medicine and,Department of Surgery, Karolinska Institutet, Stockholm, Sweden
| | - Timothy J. Kieffer
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
| | - Kate Banks
- Division of Comparative Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Jeffrey E. Pessin
- Michael F. Price Center for Genetic and Translational Medicine, Department of Medicine and Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Herbert Y. Gaisano
- Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| |
Collapse
|
14
|
Bradberry MM, Bao H, Lou X, Chapman ER. Phosphatidylinositol 4,5-bisphosphate drives Ca 2+-independent membrane penetration by the tandem C2 domain proteins synaptotagmin-1 and Doc2β. J Biol Chem 2019; 294:10942-10953. [PMID: 31147445 DOI: 10.1074/jbc.ra119.007929] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Revised: 05/28/2019] [Indexed: 12/14/2022] Open
Abstract
Exocytosis mediates the release of neurotransmitters and hormones from neurons and neuroendocrine cells. Tandem C2 domain proteins in the synaptotagmin (syt) and double C2 domain (Doc2) families regulate exocytotic membrane fusion via direct interactions with Ca2+ and phospholipid bilayers. Syt1 is a fast-acting, low-affinity Ca2+ sensor that penetrates membranes upon binding Ca2+ to trigger synchronous vesicle fusion. The closely related Doc2β is a slow-acting, high-affinity Ca2+ sensor that triggers spontaneous and asynchronous vesicle fusion, but whether it also penetrates membranes is unknown. Both syt1 and Doc2β bind the dynamically regulated plasma membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2), but it is unclear whether PIP2 serves only as a membrane contact or enables specialized membrane-binding modes by these Ca2+ sensors. Furthermore, it has been shown that PIP2 uncaging can trigger rapid, syt1-dependent exocytosis in the absence of Ca2+ influx, suggesting that current models for the action of these Ca2+ sensors are incomplete. Here, using a series of steady-state and time-resolved fluorescence measurements, we show that Doc2β, like syt1, penetrates membranes in a Ca2+-dependent manner. Unexpectedly, we observed that PIP2 can drive membrane penetration by both syt1 and Doc2β in the absence of Ca2+, providing a plausible mechanism for Ca2+-independent, PIP2-dependent exocytosis. Quantitative measurements of penetration depth revealed that, in the presence of Ca2+, PIP2 drives Doc2β, but not syt1, substantially deeper into the membrane, defining a biophysical regulatory mechanism specific to this high-affinity Ca2+ sensor. Our results provide evidence of a novel role for PIP2 in regulating, and under some circumstances triggering, exocytosis.
Collapse
Affiliation(s)
- Mazdak M Bradberry
- Howard Hughes Medical Institute and the Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706 and; Medical Scientist Training Program, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53705
| | - Huan Bao
- Howard Hughes Medical Institute and the Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706 and
| | - Xiaochu Lou
- Howard Hughes Medical Institute and the Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706 and
| | - Edwin R Chapman
- Howard Hughes Medical Institute and the Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706 and.
| |
Collapse
|
15
|
Rozov A, Bolshakov AP, Valiullina-Rakhmatullina F. The Ever-Growing Puzzle of Asynchronous Release. Front Cell Neurosci 2019; 13:28. [PMID: 30809127 PMCID: PMC6379310 DOI: 10.3389/fncel.2019.00028] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Accepted: 01/22/2019] [Indexed: 11/13/2022] Open
Abstract
Invasion of an action potential (AP) to presynaptic terminals triggers calcium dependent vesicle fusion in a relatively short time window, about a millisecond, after the onset of the AP. This allows fast and precise information transfer from neuron to neuron by means of synaptic transmission and phasic mediator release. However, at some synapses a single AP or a short burst of APs can generate delayed or asynchronous synaptic release lasting for tens or hundreds of milliseconds. Understanding the mechanisms underlying asynchronous release (AR) is important, since AR can better recruit extrasynaptic metabotropic receptors and maintain a high level of neurotransmitter in the extracellular space for a substantially longer period of time after presynaptic activity. Over the last decade substantial work has been done to identify the presynaptic calcium sensor that may be involved in AR. Several models have been suggested which may explain the long lasting presynaptic calcium elevation a prerequisite for prolonged delayed release. However, the presynaptic mechanisms underlying asynchronous vesicle release are still not well understood. In this review article, we provide an overview of the current state of knowledge on the molecular components involved in delayed vesicle fusion and in the maintenance of sufficient calcium concentration to trigger AR. In addition, we discuss possible alternative models that may explain intraterminal calcium dynamics underlying AR.
Collapse
Affiliation(s)
- Andrei Rozov
- Laboratory of Neurobiology, Institute of Fundamental Medicine and Biology, Kazan Federal University, Kazan, Russia.,Department of Physiology and Pathophysiology, University of Heidelberg, Heidelberg, Germany
| | - Alexey P Bolshakov
- Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences (RAS), Moscow, Russia.,Laboratory of Electrophysiology, Pirogov Russian National Research Medical University, Moscow, Russia
| | | |
Collapse
|
16
|
Tran HT, Anderson LH, Knight JD. Membrane-Binding Cooperativity and Coinsertion by C2AB Tandem Domains of Synaptotagmins 1 and 7. Biophys J 2019; 116:1025-1036. [PMID: 30795874 DOI: 10.1016/j.bpj.2019.01.035] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Revised: 12/21/2018] [Accepted: 01/30/2019] [Indexed: 02/04/2023] Open
Abstract
Synaptotagmin-1 (Syt-1) and synaptotagmin-7 (Syt-7) contain analogous tandem C2 domains, C2A and C2B, which together sense Ca2+ to bind membranes and promote the stabilization of exocytotic fusion pores. Syt-1 triggers fast release of neurotransmitters, whereas Syt-7 functions in processes that involve lower Ca2+ concentrations such as hormone secretion. Syt-1 C2 domains are reported to bind membranes cooperatively, based on the observation that they penetrate farther into membranes as the C2AB tandem than as individual C2 domains. In contrast, we previously suggested that the two C2 domains of Syt-7 bind membranes independently, based in part on measurements of their liposome dissociation kinetics. Here, we investigated C2A-C2B interdomain cooperativity with Syt-1 and Syt-7 using directly comparable measurements. Equilibrium Ca2+ titrations demonstrate that the Syt-7 C2AB tandem binds liposomes lacking phosphatidylinositol-4,5-bisphosphate (PIP2) with greater Ca2+ sensitivity than either of its individual domains and binds to membranes containing PIP2 even in the absence of Ca2+. Stopped-flow kinetic measurements show differences in cooperativity between Syt-1 and Syt-7: Syt-1 C2AB dissociates from PIP2-free liposomes much more slowly than either of its individual C2 domains, indicating cooperativity, whereas the major population of Syt-7 C2AB has a dissociation rate comparable to its C2A domain, suggesting a lack of cooperativity. A minor subpopulation of Syt-7 C2AB dissociates at a slower rate, which could be due to a small cooperative component and/or liposome clustering. Measurements using an environment-sensitive fluorescent probe indicate that the Syt-7 C2B domain inserts deeply into membranes as part of the C2AB tandem, similar to the coinsertion previously reported for Syt-1. Overall, coinsertion of C2A and C2B domains is coupled to cooperative energetic effects in Syt-1 to a much greater extent than in Syt-7. The difference can be understood in terms of the relative contributions of C2A and C2B domains toward membrane binding in the two proteins.
Collapse
Affiliation(s)
- Hai T Tran
- Department of Chemistry, University of Colorado Denver, Denver, Colorado
| | - Lauren H Anderson
- Department of Chemistry, University of Colorado Denver, Denver, Colorado
| | - Jefferson D Knight
- Department of Chemistry, University of Colorado Denver, Denver, Colorado.
| |
Collapse
|
17
|
Awasthi A, Ramachandran B, Ahmed S, Benito E, Shinoda Y, Nitzan N, Heukamp A, Rannio S, Martens H, Barth J, Burk K, Wang YT, Fischer A, Dean C. Synaptotagmin-3 drives AMPA receptor endocytosis, depression of synapse strength, and forgetting. Science 2018; 363:science.aav1483. [PMID: 30545844 DOI: 10.1126/science.aav1483] [Citation(s) in RCA: 83] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2018] [Accepted: 11/01/2018] [Indexed: 01/01/2023]
Abstract
Forgetting is important. Without it, the relative importance of acquired memories in a changing environment is lost. We discovered that synaptotagmin-3 (Syt3) localizes to postsynaptic endocytic zones and removes AMPA receptors from synaptic plasma membranes in response to stimulation. AMPA receptor internalization, long-term depression (LTD), and decay of long-term potentiation (LTP) of synaptic strength required calcium-sensing by Syt3 and were abolished through Syt3 knockout. In spatial memory tasks, mice in which Syt3 was knocked out learned normally but exhibited a lack of forgetting. Disrupting Syt3:GluA2 binding in a wild-type background mimicked the lack of LTP decay and lack of forgetting, and these effects were occluded in the Syt3 knockout background. Our findings provide evidence for a molecular mechanism in which Syt3 internalizes AMPA receptors to depress synaptic strength and promote forgetting.
Collapse
Affiliation(s)
- Ankit Awasthi
- Trans-synaptic Signaling Group, European Neuroscience Institute, 37077 Goettingen, Germany
| | - Binu Ramachandran
- Trans-synaptic Signaling Group, European Neuroscience Institute, 37077 Goettingen, Germany
| | - Saheeb Ahmed
- Trans-synaptic Signaling Group, European Neuroscience Institute, 37077 Goettingen, Germany
| | - Eva Benito
- German Center for Neurodegenerative Disease, 37075 Goettingen, Germany.,Department of Psychiatry and Psychotherapy, University Medical Center Goettingen, 37075 Goettingen, Germany
| | - Yo Shinoda
- Trans-synaptic Signaling Group, European Neuroscience Institute, 37077 Goettingen, Germany
| | - Noam Nitzan
- Trans-synaptic Signaling Group, European Neuroscience Institute, 37077 Goettingen, Germany
| | - Alina Heukamp
- Trans-synaptic Signaling Group, European Neuroscience Institute, 37077 Goettingen, Germany
| | - Sabine Rannio
- Trans-synaptic Signaling Group, European Neuroscience Institute, 37077 Goettingen, Germany
| | | | - Jonas Barth
- German Center for Neurodegenerative Disease, 37075 Goettingen, Germany.,Department of Psychiatry and Psychotherapy, University Medical Center Goettingen, 37075 Goettingen, Germany
| | - Katja Burk
- Trans-synaptic Signaling Group, European Neuroscience Institute, 37077 Goettingen, Germany
| | - Yu Tian Wang
- Brain Research Center and Department of Medicine, University of British Columbia, Vancouver, BC V6T2B5, Canada
| | - Andre Fischer
- German Center for Neurodegenerative Disease, 37075 Goettingen, Germany.,Department of Psychiatry and Psychotherapy, University Medical Center Goettingen, 37075 Goettingen, Germany
| | - Camin Dean
- Trans-synaptic Signaling Group, European Neuroscience Institute, 37077 Goettingen, Germany.
| |
Collapse
|
18
|
MacDougall DD, Lin Z, Chon NL, Jackman SL, Lin H, Knight JD, Anantharam A. The high-affinity calcium sensor synaptotagmin-7 serves multiple roles in regulated exocytosis. J Gen Physiol 2018; 150:783-807. [PMID: 29794152 PMCID: PMC5987875 DOI: 10.1085/jgp.201711944] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Accepted: 05/07/2018] [Indexed: 12/19/2022] Open
Abstract
MacDougall et al. review the structure and function of the calcium sensor synaptotagmin-7 in exocytosis. Synaptotagmin (Syt) proteins comprise a 17-member family, many of which trigger exocytosis in response to calcium. Historically, most studies have focused on the isoform Syt-1, which serves as the primary calcium sensor in synchronous neurotransmitter release. Recently, Syt-7 has become a topic of broad interest because of its extreme calcium sensitivity and diversity of roles in a wide range of cell types. Here, we review the known and emerging roles of Syt-7 in various contexts and stress the importance of its actions. Unique functions of Syt-7 are discussed in light of recent imaging, electrophysiological, and computational studies. Particular emphasis is placed on Syt-7–dependent regulation of synaptic transmission and neuroendocrine cell secretion. Finally, based on biochemical and structural data, we propose a mechanism to link Syt-7’s role in membrane fusion with its role in subsequent fusion pore expansion via strong calcium-dependent phospholipid binding.
Collapse
Affiliation(s)
| | - Zesen Lin
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | - Nara L Chon
- Department of Chemistry, University of Colorado, Denver, CO
| | - Skyler L Jackman
- Vollum Institute, Oregon Health & Science University, Portland, OR
| | - Hai Lin
- Department of Chemistry, University of Colorado, Denver, CO
| | | | - Arun Anantharam
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| |
Collapse
|
19
|
Huang C, Walker EM, Dadi PK, Hu R, Xu Y, Zhang W, Sanavia T, Mun J, Liu J, Nair GG, Tan HYA, Wang S, Magnuson MA, Stoeckert CJ, Hebrok M, Gannon M, Han W, Stein R, Jacobson DA, Gu G. Synaptotagmin 4 Regulates Pancreatic β Cell Maturation by Modulating the Ca 2+ Sensitivity of Insulin Secretion Vesicles. Dev Cell 2018; 45:347-361.e5. [PMID: 29656931 PMCID: PMC5962294 DOI: 10.1016/j.devcel.2018.03.013] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Revised: 02/12/2018] [Accepted: 03/19/2018] [Indexed: 12/14/2022]
Abstract
Islet β cells from newborn mammals exhibit high basal insulin secretion and poor glucose-stimulated insulin secretion (GSIS). Here we show that β cells of newborns secrete more insulin than adults in response to similar intracellular Ca2+ concentrations, suggesting differences in the Ca2+ sensitivity of insulin secretion. Synaptotagmin 4 (Syt4), a non-Ca2+ binding paralog of the β cell Ca2+ sensor Syt7, increased by ∼8-fold during β cell maturation. Syt4 ablation increased basal insulin secretion and compromised GSIS. Precocious Syt4 expression repressed basal insulin secretion but also impaired islet morphogenesis and GSIS. Syt4 was localized on insulin granules and Syt4 levels inversely related to the number of readily releasable vesicles. Thus, transcriptional regulation of Syt4 affects insulin secretion; Syt4 expression is regulated in part by Myt transcription factors, which repress Syt4 transcription. Finally, human SYT4 regulated GSIS in EndoC-βH1 cells, a human β cell line. These findings reveal the role that altered Ca2+ sensing plays in regulating β cell maturation.
Collapse
Affiliation(s)
- Chen Huang
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA; Center for Stem Cell Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA; The Program of Developmental Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA
| | - Emily M Walker
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA
| | - Prasanna K Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA
| | - Ruiying Hu
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA; Center for Stem Cell Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA; The Program of Developmental Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA
| | - Yanwen Xu
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA; Center for Stem Cell Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA; The Program of Developmental Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA
| | - Wenjian Zhang
- China-Japan Friendship Hospital, Beijing 100029, P. R. China
| | - Tiziana Sanavia
- Department of Biomedical Informatics, Harvard Medical School, Boston, MA 02115, USA
| | - Jisoo Mun
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA
| | - Jennifer Liu
- Diabetes Center, UCSF, San Francisco, CA 94143, USA
| | | | - Hwee Yim Angeline Tan
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, Singapore, Singapore
| | - Sui Wang
- Department of Ophthalmology, Mary M. and Sash A. Spencer Center for Vision Research, Stanford University School of Medicine, Palo Alto, CA 94304, USA
| | - Mark A Magnuson
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA; Center for Stem Cell Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA; Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA
| | - Christian J Stoeckert
- Institute for Biomedical Informatics and Department of Genetics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
| | | | - Maureen Gannon
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA; Center for Stem Cell Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA; The Program of Developmental Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA; Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA; Department of Medicine, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA
| | - Weiping Han
- Laboratory of Metabolic Medicine, Singapore Bioimaging Consortium, Singapore, Singapore
| | - Roland Stein
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA
| | - David A Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA.
| | - Guoqiang Gu
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA; Center for Stem Cell Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA; The Program of Developmental Biology, Vanderbilt University School of Medicine, Department of Veterans Affairs, Tennessee Valley Health Authority, Nashville, TN 37232, USA.
| |
Collapse
|
20
|
Sheng B, Jiang Y, Wu D, Lai N, Ye Z, Zhang B, Fang X, Xu S. RNAi-mediated SYT14 knockdown inhibits the growth of human glioma cell line U87MG. Brain Res Bull 2018; 140:60-64. [PMID: 29634997 DOI: 10.1016/j.brainresbull.2018.04.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2017] [Revised: 12/04/2017] [Accepted: 04/04/2018] [Indexed: 10/17/2022]
Abstract
SYT14 (Synaptotagmin 14) participates in pathomechanical neurodegeneration and contributes to abnormal neurodevelopment. However, the functional mechanism of SYT14 in human glioma tumorigenesis remains unclear. In the present study, we measured the expression levels of SYT14 mRNA in human glioma cell lines, U373MG, U178, and U87MG and neural stem cells (NSC) cell line by RT-PCR, and used lentivirus-mediated small hairpin RNAs (shRNAs) to knock down SYT14 expression in U87MG cells. Changes in SYT14 expression were determined by real-time PCR. Cell proliferation and colony formation assays were used to analyze the role of SYT14 in U87MG cell proliferation, and cell apoptosis was assessed by flow cytometry. SYT14 mRNA expression was detected in the three glioma cell lines, and was highest in the U87MG cell line. The RNAi-mediated knockdown of SYT14 significantly decreased cell proliferation and colony formation in U87MG cells, and caused a moderate increase in apoptosis. Fewer S phase cells and more G2/M phase cells were observed. These data indicate that SYT14 is highly expressed in glioma cells, and may participate in glioma cell proliferation, apoptosis, and colony formation.
Collapse
Affiliation(s)
- Bin Sheng
- Department of Neurosurgery, The First Affiliated Hospital of Wannan Medical College, Wuhu City, Anhui, 241001, China
| | - Yuxin Jiang
- Department of Physiology, School of Basic Medicine, Wannan Medical College, Wuhu City, Anhui, 241000, China
| | - Degang Wu
- Department of Neurosurgery, The First Affiliated Hospital of Wannan Medical College, Wuhu City, Anhui, 241001, China
| | - Niansheng Lai
- Department of Neurosurgery, The First Affiliated Hospital of Wannan Medical College, Wuhu City, Anhui, 241001, China
| | - Zhennan Ye
- Department of Neurosurgery, The Second Affiliated Hospital of Guangzhou Medical University, Guangzhou City, Guangdong, 510000, China
| | - Bingbing Zhang
- Department of Neurosurgery, The First Affiliated Hospital of Wannan Medical College, Wuhu City, Anhui, 241001, China
| | - Xinggen Fang
- Department of Neurosurgery, The First Affiliated Hospital of Wannan Medical College, Wuhu City, Anhui, 241001, China.
| | - Shanshui Xu
- Department of Neurosurgery, The First Affiliated Hospital of Wannan Medical College, Wuhu City, Anhui, 241001, China.
| |
Collapse
|
21
|
Rao TC, Santana Rodriguez Z, Bradberry MM, Ranski AH, Dahl PJ, Schmidtke MW, Jenkins PM, Axelrod D, Chapman ER, Giovannucci DR, Anantharam A. Synaptotagmin isoforms confer distinct activation kinetics and dynamics to chromaffin cell granules. J Gen Physiol 2017; 149:763-780. [PMID: 28687607 PMCID: PMC5560776 DOI: 10.1085/jgp.201711757] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Revised: 05/15/2017] [Accepted: 06/12/2017] [Indexed: 01/09/2023] Open
Abstract
Chromaffin cells release transmitters from populations of granules to which synaptotagmin-1 and synaptotagmin-7 are selectively sorted. Rao et al. characterize the functional properties of these granules and show that synaptotagmin-7 confers fast kinetics and high efficacy to the exocytotic event. Adrenomedullary chromaffin cells respond to sympathetic nervous system activation by secreting a cocktail of potent neuropeptides and hormones into the circulation. The distinct phases of the chromaffin cell secretory response have been attributed to the progressive fusion of distinct populations of dense core granules with different activation kinetics. However, it has been difficult to define what distinguishes these populations at the molecular level. Functional segregation of granule pools may depend on selective sorting of synaptotagmin-1 (Syt-1) and synaptotagmin-7 (Syt-7), which our previous work showed are rarely cosorted to the same granule. Here we assess the consequences of selective sorting of Syt isoforms in chromaffin cells, particularly with respect to granule dynamics and activation kinetics. Upon depolarization of cells expressing fluorescent Syt isoforms using elevated K+, we find that Syt-7 granules fuse with faster kinetics than Syt-1 granules, irrespective of stimulation strength. Pharmacological blockade of Ca2+ channels reveals differential dependence of Syt-1 versus Syt-7 granule exocytosis on Ca2+ channel subtypes. Syt-7 granules also show a greater tendency to fuse in clusters than Syt-1 granules, and granules harboring Syt-1 travel a greater distance before fusion than those with Syt-7, suggesting that there is spatial and fusion-site heterogeneity among the two granule populations. However, the greatest functional difference between granule populations is their responsiveness to Ca2+. Upon introduction of Ca2+ into permeabilized cells, Syt-7 granules fuse with fast kinetics and high efficacy, even at low Ca2+ levels (e.g., when cells are weakly stimulated). Conversely, Syt-1 granules require a comparatively larger increase in intracellular Ca2+ for activation. At Ca2+ concentrations above 30 µM, activation kinetics are faster for Syt-1 granules than for Syt-7 granules. Our study provides evidence for functional specialization of chromaffin cell granules via selective expression of Syt isoforms with different Ca2+ sensitivities.
Collapse
Affiliation(s)
- Tejeshwar C Rao
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | | | - Mazdak M Bradberry
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin, Madison, WI
| | | | - Peter J Dahl
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | | | - Paul M Jenkins
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | - Daniel Axelrod
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | - Edwin R Chapman
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin, Madison, WI
| | - David R Giovannucci
- Department of Neurosciences, University of Toledo Medical School, Toledo, OH
| | - Arun Anantharam
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| |
Collapse
|
22
|
Gavrin A, Kulikova O, Bisseling T, Fedorova EE. Interface Symbiotic Membrane Formation in Root Nodules of Medicago truncatula: the Role of Synaptotagmins MtSyt1, MtSyt2 and MtSyt3. FRONTIERS IN PLANT SCIENCE 2017; 8:201. [PMID: 28265280 PMCID: PMC5316549 DOI: 10.3389/fpls.2017.00201] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Accepted: 02/02/2017] [Indexed: 05/23/2023]
Abstract
UNLABELLED Symbiotic bacteria (rhizobia) are maintained and conditioned to fix atmospheric nitrogen in infected cells of legume root nodules. Rhizobia are confined to the asymmetrical protrusions of plasma membrane (PM): infection threads (IT), cell wall-free unwalled droplets and symbiosomes. These compartments rapidly increase in surface and volume due to the microsymbiont expansion, and remarkably, the membrane resources of the host cells are targeted to interface membrane quite precisely. We hypothesized that the change in the membrane tension around the expanding microsymbionts creates a vector for membrane traffic toward the symbiotic interface. To test this hypothesis, we selected calcium sensors from the group of synaptotagmins: MtSyt1, Medicago truncatula homolog of AtSYT1 from Arabidopsis thaliana known to be involved in membrane repair, and two other homologs expressed in root nodules: MtSyt2 and MtSyt3. Here we show that MtSyt1, MtSyt2, and MtSyt3 are expressed in the expanding cells of the meristem, zone of infection and proximal cell layers of zone of nitrogen fixation (MtSyt1, MtSyt3). All three GFP-tagged proteins delineate the interface membrane of IT and unwalled droplets and create a subcompartments of PM surrounding these structures. The localization of MtSyt1 by EM immunogold labeling has shown the signal on symbiosome membrane and endoplasmic reticulum (ER). To specify the role of synaptotagmins in interface membrane formation, we compared the localization of MtSyt1, MtSyt3 and exocyst subunit EXO70i, involved in the tethering of post-Golgi secretory vesicles and operational in tip growth. The localization of EXO70i in root nodules and arbusculated roots was strictly associated with the tips of IT and the tips of arbuscular fine branches, but the distribution of synaptotagmins on membrane subcompartments was broader and includes lateral parts of IT, the membrane of unwalled droplets as well as the symbiosomes. The double silencing of synaptotagmins caused a delay in rhizobia release and blocks symbiosome maturation confirming the functional role of synaptotagmins. IN CONCLUSION synaptotagmin-dependent membrane fusion along with tip-targeted exocytosis is operational in the formation of symbiotic interface.
Collapse
Affiliation(s)
- Aleksandr Gavrin
- Laboratory of Molecular Biology, Department of Plant Sciences, Graduate School Experimental Plant Sciences, Wageningen UniversityWageningen, Netherlands
- Sainsbury Laboratory, University of CambridgeCambridge, UK
| | - Olga Kulikova
- Laboratory of Molecular Biology, Department of Plant Sciences, Graduate School Experimental Plant Sciences, Wageningen UniversityWageningen, Netherlands
| | - Ton Bisseling
- Laboratory of Molecular Biology, Department of Plant Sciences, Graduate School Experimental Plant Sciences, Wageningen UniversityWageningen, Netherlands
| | - Elena E. Fedorova
- Laboratory of Molecular Biology, Department of Plant Sciences, Graduate School Experimental Plant Sciences, Wageningen UniversityWageningen, Netherlands
| |
Collapse
|
23
|
Wolfes AC, Ahmed S, Awasthi A, Stahlberg MA, Rajput A, Magruder DS, Bonn S, Dean C. A novel method for culturing stellate astrocytes reveals spatially distinct Ca2+ signaling and vesicle recycling in astrocytic processes. J Gen Physiol 2016; 149:149-170. [PMID: 27908976 PMCID: PMC5217085 DOI: 10.1085/jgp.201611607] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Revised: 11/09/2016] [Accepted: 11/11/2016] [Indexed: 12/20/2022] Open
Abstract
Communication between astrocytes and neurons has been difficult to study because cultured astrocytes do not resemble those in vivo. Wolfes et al. develop a stellate astrocyte monoculture with physiological characteristics and find that VAMP2 and SYT7 mark distinct vesicle populations in astrocytes. Interactions between astrocytes and neurons rely on the release and uptake of glial and neuronal molecules. But whether astrocytic vesicles exist and exocytose in a regulated or constitutive fashion is under debate. The majority of studies have relied on indirect methods or on astrocyte cultures that do not resemble stellate astrocytes found in vivo. Here, to investigate vesicle-associated proteins and exocytosis in stellate astrocytes specifically, we developed a simple, fast, and economical method for growing stellate astrocyte monocultures. This method is superior to other monocultures in terms of astrocyte morphology, mRNA expression profile, protein expression of cell maturity markers, and Ca2+ fluctuations: In astrocytes transduced with GFAP promoter–driven Lck-GCaMP3, spontaneous Ca2+ events in distinct domains (somata, branchlets, and microdomains) are similar to those in astrocytes co-cultured with other glia and neurons but unlike Ca2+ events in astrocytes prepared using the McCarthy and de Vellis (MD) method and immunopanned (IP) astrocytes. We identify two distinct populations of constitutively recycling vesicles (harboring either VAMP2 or SYT7) specifically in branchlets of cultured stellate astrocytes. SYT7 is developmentally regulated in these astrocytes, and we observe significantly fewer synapses in wild-type mouse neurons grown on Syt7−/− astrocytes. SYT7 may thus be involved in trafficking or releasing synaptogenic factors. In summary, our novel method yields stellate astrocyte monocultures that can be used to study Ca2+ signaling and vesicle recycling and dynamics in astrocytic processes.
Collapse
Affiliation(s)
- Anne C Wolfes
- Trans-Synaptic Signaling Group, European Neuroscience Institute Göttingen, 37077 Göttingen, Germany
| | - Saheeb Ahmed
- Trans-Synaptic Signaling Group, European Neuroscience Institute Göttingen, 37077 Göttingen, Germany
| | - Ankit Awasthi
- Trans-Synaptic Signaling Group, European Neuroscience Institute Göttingen, 37077 Göttingen, Germany
| | - Markus A Stahlberg
- Trans-Synaptic Signaling Group, European Neuroscience Institute Göttingen, 37077 Göttingen, Germany
| | - Ashish Rajput
- Research Group for Computational Systems Biology, German Center for Neurodegenerative Disease (DZNE), 37075 Göttingen, Germany
| | - Daniel S Magruder
- Research Group for Computational Systems Biology, German Center for Neurodegenerative Disease (DZNE), 37075 Göttingen, Germany
| | - Stefan Bonn
- Research Group for Computational Systems Biology, German Center for Neurodegenerative Disease (DZNE), 37075 Göttingen, Germany
| | - Camin Dean
- Trans-Synaptic Signaling Group, European Neuroscience Institute Göttingen, 37077 Göttingen, Germany
| |
Collapse
|
24
|
Dolai S, Xie L, Zhu D, Liang T, Qin T, Xie H, Kang Y, Chapman ER, Gaisano HY. Synaptotagmin-7 Functions to Replenish Insulin Granules for Exocytosis in Human Islet β-Cells. Diabetes 2016; 65:1962-76. [PMID: 27207520 PMCID: PMC5384637 DOI: 10.2337/db15-1436] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/19/2015] [Accepted: 04/16/2016] [Indexed: 12/13/2022]
Abstract
Synaptotagmin (Syt)-7, a major component of the exocytotic machinery in neurons, is also the major Syt in rodent pancreatic β-cells shown to mediate glucose-stimulated insulin secretion (GSIS). However, Syt-7's precise exocytotic actions in β-cells remain unknown. We show that Syt-7 is abundant in human β-cells. Adenovirus-short hairpin RNA knockdown (KD) of Syt-7 in human islets reduced first- and second-phase GSIS attributed to the reduction of exocytosis of predocked and newcomer insulin secretory granules (SGs). Glucose stimulation expectedly induced Syt-7 association in a Ca(2+)-dependent manner with syntaxin-3 and syntaxin-1A soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes known to mediate exocytosis of newcomer and predocked SGs, respectively. However, Syt-7-KD did not disrupt SNARE complex assembly. Instead, electron microscopy analysis showed that Syt-7-KD reduced the recruitment of SGs to the plasma membrane after glucose-stimulated depletion, which could not be rescued by glucagon-like peptide 1 pretreatment. To assess the possibility that this new action of Syt-7 on SG recruitment may involve calmodulin (CaM), pretreatment of islets with CaM blocker calmidazolium showed effects very similar to those of Syt-7-KD. Syt-7 therefore plays a novel more dominant function in the replenishment of releasable SG pools in human β-cells than its previously purported role in exocytotic fusion per se.
Collapse
Affiliation(s)
- Subhankar Dolai
- Department of Medicine, University of Toronto, Toronto, ON, Canada
| | - Li Xie
- Department of Medicine, University of Toronto, Toronto, ON, Canada
| | - Dan Zhu
- Department of Medicine, University of Toronto, Toronto, ON, Canada
| | - Tao Liang
- Department of Medicine, University of Toronto, Toronto, ON, Canada
| | - Tairan Qin
- Department of Medicine, University of Toronto, Toronto, ON, Canada
| | - Huanli Xie
- Department of Medicine, University of Toronto, Toronto, ON, Canada
| | - Youhou Kang
- Department of Medicine, University of Toronto, Toronto, ON, Canada
| | - Edwin R Chapman
- Department of Neuroscience, Howard Hughes Medical Institute, University of Wisconsin-Madison, Madison, WI
| | - Herbert Y Gaisano
- Department of Medicine, University of Toronto, Toronto, ON, Canada Department of Physiology, University of Toronto, Toronto, ON, Canada
| |
Collapse
|
25
|
Wang H, Han S, Siao W, Song C, Xiang Y, Wu X, Cheng P, Li H, Jásik J, Mičieta K, Turňa J, Voigt B, Baluška F, Liu J, Wang Y, Zhao H. Arabidopsis Synaptotagmin 2 Participates in Pollen Germination and Tube Growth and Is Delivered to Plasma Membrane via Conventional Secretion. MOLECULAR PLANT 2015; 8:1737-50. [PMID: 26384245 DOI: 10.1016/j.molp.2015.09.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Revised: 08/18/2015] [Accepted: 09/05/2015] [Indexed: 05/15/2023]
Abstract
Arabidopsis synaptotagmin 2 (SYT2) has been reported to participate in an unconventional secretory pathway in somatic cells. Our results showed that SYT2 was expressed mainly in the pollen of Arabidopsis thaliana. The pollen of syt2 T-DNA and RNA interference mutant lines exhibited reduced total germination and impeded pollen tube growth. Analysis of the expression of SYT2-GFP fusion protein in the pollen tube indicates that SYT2 was localized to distinct, patchy compartments but could co-localize with the Golgi markers, BODIPY TR C5 ceramide and GmMan1-mCherry. However, SYT2-DsRed-E5 was localized to the plasma membrane in Arabidopsis suspension cells, in addition to the Golgi apparatus. The localization of SYT2 at the plasma membrane was further supported by immunofluorescence staining in pollen tubes. Moreover, brefeldin A treatment inhibited the transport of SYT2 to the plasma membrane and caused SYT2 to aggregate and form enlarged compartments. Truncation of the SYT2-C2AB domains also resulted in retention of SYT2 in the Golgi apparatus. An in vitro phospholipid-binding assay showed that SYT2-C2AB domains bind to the phospholipid membrane in a calcium-dependent manner. Take together, our results indicated that SYT2 was required for pollen germination and pollen tube growth, and was involved in conventional exocytosis.
Collapse
Affiliation(s)
- Hui Wang
- Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Science, Beijing Normal University, Beijing 100875, China
| | - Shengcheng Han
- Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Science, Beijing Normal University, Beijing 100875, China
| | - Wei Siao
- Department of Plant Cell Biology, IZMB, University of Bonn, Kirschallee 1, 53115 Bonn, Germany
| | - Chunqing Song
- Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Science, Beijing Normal University, Beijing 100875, China
| | - Yun Xiang
- School of Life Science, Lanzhou University, Lanzhou 730000, China
| | - Xiaorong Wu
- School of Life Science, Lanzhou University, Lanzhou 730000, China
| | - Pengyu Cheng
- Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Science, Beijing Normal University, Beijing 100875, China
| | - Hongjuan Li
- Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Science, Beijing Normal University, Beijing 100875, China
| | - Ján Jásik
- Comenius University Science Park, Comenius University, Bratislava, Mlynská dolina, 842 15 Bratislava 4, Slovakia
| | - Karol Mičieta
- Department of Botany, Faculty of Natural Sciences, Comenius University, Révová 39, 811 02 Bratislava 1, Slovakia
| | - Ján Turňa
- Department of Molecular Biology, Comenius University, Faculty of Natural Sciences, Mlynská dolina, pavilion B-2, 842 15 Bratislava 4, Slovakia
| | - Boris Voigt
- Department of Plant Cell Biology, IZMB, University of Bonn, Kirschallee 1, 53115 Bonn, Germany
| | - František Baluška
- Department of Plant Cell Biology, IZMB, University of Bonn, Kirschallee 1, 53115 Bonn, Germany; Institute of Botany, Slovak Academy of Sciences, Dubravska cesta 9, SK-84523 Bratislava, Slovak Republic.
| | - Jin Liu
- Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Science, Beijing Normal University, Beijing 100875, China
| | - Yingdian Wang
- Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Science, Beijing Normal University, Beijing 100875, China
| | - Heping Zhao
- Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Science, Beijing Normal University, Beijing 100875, China.
| |
Collapse
|
26
|
Role of Munc13-4 as a Ca2+-dependent tether during platelet secretion. Biochem J 2015; 473:627-39. [PMID: 26637270 DOI: 10.1042/bj20151150] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Accepted: 12/04/2015] [Indexed: 11/17/2022]
Abstract
The Munc13 family of exocytosis regulators has multiple Ca(2+)-binding, C2 domains. Here, we probed the mechanism by which Munc13-4 regulates in vitro membrane fusion and platelet exocytosis. We show that Munc13-4 enhances in vitro soluble NSF attachment protein receptor (SNARE)-dependent, proteoliposome fusion in a Ca(2+)- and phosphatidylserine (PS)-dependent manner that was independent of SNARE concentrations. Munc13-4-SNARE interactions, under the conditions used, were minimal in the absence or presence of Ca(2+). However, Munc13-4 was able to bind and cluster liposomes harbouring PS in response to Ca(2+). Interestingly, Ca(2+)-dependent liposome binding/clustering and enhancement of proteoliposome fusion required both Munc13-4 C2 domains, but only the Ca(2+)-liganding aspartate residues of the C2B domain. Analytical ultracentrifugation (AUC) measurements indicated that, in solution, Munc13-4 was a monomeric prolate ellipsoid with dimensions consistent with a molecule that could bridge two fusing membranes. To address the potential role of Munc13-4 as a tethering protein in platelets, we examined mepacrine-stained, dense granule mobility and secretion in platelets from wild-type and Munc13-4 null (Unc13d(Jinx)) mice. In the absence of Munc13-4, dense granules were highly mobile in both resting and stimulated platelets, and stimulation-dependent granule release was absent. These observations suggest that dense granules are stably docked in resting platelets awaiting stimulation and that Munc13-4 plays a vesicle-stabilizing or tethering role in resting platelets and also in activated platelets in response to Ca(2+). In summary, we show that Munc13-4 conveys Ca(2+) sensitivity to platelet SNARE-mediated membrane fusion and reveal a potential mechanism by which Munc13-4 bridges and stabilizes apposing membranes destined for fusion.
Collapse
|
27
|
Abstract
UNLABELLED The Ca(2+) sensor synaptotagmin-1 (syt-1) regulates neurotransmitter release by interacting with anionic phospholipids. Here we test the idea that the intrinsic kinetics of syt-membrane interactions determine, in part, the time course of synaptic transmission. To tune the kinetics of this interaction, we grafted structural elements from the slowest isoform, syt-7, onto the fastest isoform, syt-1, resulting in a chimera with intermediate kinetic properties. Moreover, the chimera coupled a physiologically irrelevant metal, Sr(2+), to membrane fusion in vitro. When substituted for syt-1 in mouse hippocampal neurons, the chimera slowed the kinetics of synaptic transmission. Neurons expressing the chimera also evinced rapid and efficient Sr(2+) triggered release, in contrast to the weak response of neurons expressing syt-1. These findings reveal presynaptic sensor-membrane interactions as a major factor regulating the speed of the release machinery. Finally, the chimera failed to clamp the elevated spontaneous fusion rate exhibited by syt-1 KO neurons, indicating that the metal binding loops of syt-1 regulate the two modes of release by distinct mechanisms. SIGNIFICANCE STATEMENT In calcium, synaptotagmin-1 triggers neurotransmitter release by interacting with membranes. Here, we demonstrate that intrinsic properties of this interaction control the time course of synaptic transmission. We engineered a "chimera" using synaptotagmin-1 and elements of a slower isoform, synaptotagmin-7. When expressed in neurons, the chimera slowed the rate of neurotransmitter release. Furthermore, unlike native synaptotagmin-1, the chimera was able to function robustly in the presence of strontium-a metal not present in cells. We exploited this ability to show that a key function of synaptotagmin-1 is to penetrate cell membranes. This work sheds light on fundamental mechanisms of neurotransmitter release.
Collapse
|
28
|
Sex-specific regulation of follicle-stimulating hormone secretion by synaptotagmin 9. Nat Commun 2015; 6:8645. [PMID: 26482442 PMCID: PMC4620939 DOI: 10.1038/ncomms9645] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Accepted: 09/11/2015] [Indexed: 12/24/2022] Open
Abstract
The anterior pituitary releases six different hormones that control virtually all aspects of vertebrate physiology, yet the molecular mechanisms underlying their Ca(2+)-triggered release remain unknown. A subset of the synaptotagmin (syt) family of proteins serve as Ca(2+) sensors for exocytosis in neurons and neuroendocrine cells, and are thus likely to regulate pituitary hormone secretion. Here we show that numerous syt isoforms are highly expressed in the pituitary gland in a lobe, and sex-specific manner. We further investigated a Ca(2+)-activated isoform, syt-9, and found that it is expressed in a subpopulation of anterior pituitary cells, the gonadotropes. Follicle-stimulating hormone (FSH) and syt-9 are highly co-localized in female, but not male, mice. Loss of syt-9 results in diminished basal and stimulated FSH secretion only in females, resulting in alterations in the oestrus cycle. This work uncovers a new function for syt-9 and reveals a novel sex difference in reproductive hormone secretion.
Collapse
|
29
|
Chon NL, Osterberg JR, Henderson J, Khan HM, Reuter N, Knight JD, Lin H. Membrane Docking of the Synaptotagmin 7 C2A Domain: Computation Reveals Interplay between Electrostatic and Hydrophobic Contributions. Biochemistry 2015; 54:5696-711. [DOI: 10.1021/acs.biochem.5b00422] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- Nara Lee Chon
- Department
of Chemistry, University of Colorado Denver, Denver, Colorado 80217-3364, United States
| | - J. Ryan Osterberg
- Department
of Chemistry, University of Colorado Denver, Denver, Colorado 80217-3364, United States
| | - Jack Henderson
- Department
of Chemistry, University of Colorado Denver, Denver, Colorado 80217-3364, United States
| | - Hanif M. Khan
- Department
of Molecular Biology, University of Bergen, 5008 Bergen, Norway
- Computational
Biology Unit, Department of Informatics, University of Bergen, 5008 Bergen, Norway
| | - Nathalie Reuter
- Department
of Molecular Biology, University of Bergen, 5008 Bergen, Norway
- Computational
Biology Unit, Department of Informatics, University of Bergen, 5008 Bergen, Norway
| | - Jefferson D. Knight
- Department
of Chemistry, University of Colorado Denver, Denver, Colorado 80217-3364, United States
| | - Hai Lin
- Department
of Chemistry, University of Colorado Denver, Denver, Colorado 80217-3364, United States
| |
Collapse
|
30
|
Osterberg JR, Chon NL, Boo A, Maynard FA, Lin H, Knight JD. Membrane Docking of the Synaptotagmin 7 C2A Domain: Electron Paramagnetic Resonance Measurements Show Contributions from Two Membrane Binding Loops. Biochemistry 2015; 54:5684-95. [PMID: 26322740 DOI: 10.1021/acs.biochem.5b00421] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The synaptotagmin (Syt) family of proteins plays an important role in vesicle docking and fusion during Ca(2+)-induced exocytosis in a wide variety of cell types. Its role as a Ca(2+) sensor derives primarily from its two C2 domains, C2A and C2B, which insert into anionic lipid membranes upon binding Ca(2+). Syt isoforms 1 and 7 differ significantly in their Ca(2+) sensitivity; the C2A domain from Syt7 binds Ca(2+) and membranes much more tightly than the C2A domain from Syt1, at least in part because of greater contributions from the hydrophobic effect. While the structure and membrane activity of Syt1 have been extensively studied, the structural origins of differences between Syt1 and Syt7 are unknown. This study used site-directed spin labeling and electron paramagnetic resonance spectroscopy to determine depth parameters for the Syt7 C2A domain, for comparison to analogous previous measurements with the Syt1 C2A domain. In a novel approach, the membrane docking geometry of both Syt1 and Syt7 C2A was modeled by mapping depth parameters onto multiple molecular dynamics-simulated structures of the Ca(2+)-bound protein. The models reveal membrane penetration of Ca(2+) binding loops 1 (CBL1) and 3 (CBL3), and membrane binding is more sensitive to mutations in CBL3. On average, Syt7 C2A inserts more deeply into the membrane than Syt1 C2A, although depths vary among the different structural models. This observation provides a partial structural explanation for the hydrophobically driven membrane docking of Syt7 C2A.
Collapse
Affiliation(s)
- J Ryan Osterberg
- Department of Chemistry, University of Colorado Denver , Denver, Colorado 80217, United States
| | - Nara Lee Chon
- Department of Chemistry, University of Colorado Denver , Denver, Colorado 80217, United States
| | - Arthur Boo
- Department of Chemistry, University of Colorado Denver , Denver, Colorado 80217, United States
| | - Favinn A Maynard
- Department of Chemistry, University of Colorado Denver , Denver, Colorado 80217, United States
| | - Hai Lin
- Department of Chemistry, University of Colorado Denver , Denver, Colorado 80217, United States
| | - Jefferson D Knight
- Department of Chemistry, University of Colorado Denver , Denver, Colorado 80217, United States
| |
Collapse
|
31
|
Vasquez JK, Chantranuvatana K, Giardina DT, Coffman MD, Knight JD. Lateral diffusion of proteins on supported lipid bilayers: additive friction of synaptotagmin 7 C2A-C2B tandem domains. Biochemistry 2014; 53:7904-13. [PMID: 25437758 PMCID: PMC4278679 DOI: 10.1021/bi5012223] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
![]()
The
synaptotagmin (Syt) family of proteins contains tandem C2 domains,
C2A and C2B, which bind membranes in the presence of Ca2+ to trigger vesicle fusion during exocytosis. Despite recent progress,
the role and extent of interdomain interactions between C2A and C2B
in membrane binding remain unclear. To test whether the two domains
interact on a planar lipid bilayer (i.e., experience thermodynamic
interdomain contacts), diffusion of fluorescent-tagged C2A, C2B, and
C2AB domains from human Syt7 was measured using total internal reflection
fluorescence microscopy with single-particle tracking. The C2AB tandem
exhibits a lateral diffusion constant approximately half the value
of the isolated single domains and does not change when additional
residues are engineered into the C2A–C2B linker. This is the
expected result if C2A and C2B are separated when membrane-bound;
theory predicts that C2AB diffusion would be faster if the two domains
were close enough together to have interdomain contact. Stopped-flow
measurements of membrane dissociation kinetics further support an
absence of interdomain interactions, as dissociation kinetics of the
C2AB tandem remain unchanged when rigid or flexible linker extensions
are included. Together, the results suggest that the two C2 domains
of Syt7 bind independently to planar membranes, in contrast to reported
interdomain cooperativity in Syt1.
Collapse
Affiliation(s)
- Joseph K Vasquez
- Department of Chemistry, University of Colorado Denver , Denver, Colorado 80217, United States
| | | | | | | | | |
Collapse
|
32
|
Liu H, Bai H, Xue R, Takahashi H, Edwardson JM, Chapman ER. Linker mutations reveal the complexity of synaptotagmin 1 action during synaptic transmission. Nat Neurosci 2014; 17:670-7. [PMID: 24657966 PMCID: PMC4139111 DOI: 10.1038/nn.3681] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Accepted: 02/21/2014] [Indexed: 12/13/2022]
Abstract
The Ca(2+) sensor for rapid synaptic vesicle exocytosis, synaptotagmin 1 (syt), is largely composed of two Ca(2+)-sensing C2 domains, C2A and C2B. We investigated the apparent synergy between the tandem C2 domains by altering the length and rigidity of the linker that connects them. The behavior of the linker mutants revealed a correlation between the ability of the C2 domains to penetrate membranes in response to Ca(2+) and to drive evoked neurotransmitter release in cultured mouse neurons, uncovering a step in excitation-secretion coupling. Using atomic force microscopy, we found that the synergy between these C2 domains involved intra-molecular interactions between them. Thus, syt function is markedly affected by changes in the physical nature of the linker that connects its tandem C2 domains. Moreover, the linker mutations uncoupled syt-mediated regulation of evoked and spontaneous release, revealing that syt also acts as a fusion clamp before the Ca(2+) trigger.
Collapse
Affiliation(s)
- Huisheng Liu
- 1] Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, USA. [2] [3]
| | - Hua Bai
- 1] Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, USA. [2]
| | - Renhao Xue
- Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, USA
| | | | | | - Edwin R Chapman
- Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, USA
| |
Collapse
|
33
|
Liu H, Bai H, Hui E, Yang L, Evans CS, Wang Z, Kwon SE, Chapman ER. Synaptotagmin 7 functions as a Ca2+-sensor for synaptic vesicle replenishment. eLife 2014; 3:e01524. [PMID: 24569478 PMCID: PMC3930910 DOI: 10.7554/elife.01524] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Synaptotagmin (syt) 7 is one of three syt isoforms found in all metazoans; it is ubiquitously expressed, yet its function in neurons remains obscure. Here, we resolved Ca(2+)-dependent and Ca(2+)-independent synaptic vesicle (SV) replenishment pathways, and found that syt 7 plays a selective and critical role in the Ca(2+)-dependent pathway. Mutations that disrupt Ca(2+)-binding to syt 7 abolish this function, suggesting that syt 7 functions as a Ca(2+)-sensor for replenishment. The Ca(2+)-binding protein calmodulin (CaM) has also been implicated in SV replenishment, and we found that loss of syt 7 was phenocopied by a CaM antagonist. Moreover, we discovered that syt 7 binds to CaM in a highly specific and Ca(2+)-dependent manner; this interaction requires intact Ca(2+)-binding sites within syt 7. Together, these data indicate that a complex of two conserved Ca(2+)-binding proteins, syt 7 and CaM, serve as a key regulator of SV replenishment in presynaptic nerve terminals. DOI: http://dx.doi.org/10.7554/eLife.01524.001.
Collapse
Affiliation(s)
- Huisheng Liu
- Department of Neuroscience, Howard Hughes Medical Institute, University of Wisconsin-Madison, Madison, United States
| | | | | | | | | | | | | | | |
Collapse
|
34
|
Lyakhova TA, Knight JD. The C2 domains of granuphilin are high-affinity sensors for plasma membrane lipids. Chem Phys Lipids 2013; 182:29-37. [PMID: 24184645 DOI: 10.1016/j.chemphyslip.2013.10.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Revised: 09/30/2013] [Accepted: 10/19/2013] [Indexed: 11/30/2022]
Abstract
Membrane-targeting proteins are crucial components of many cell signaling pathways, including the secretion of insulin. Granuphilin, also known as synaptotagmin-like protein 4, functions in tethering secretory vesicles to the plasma membrane prior to exocytosis. Granuphilin docks to insulin secretory vesicles through interaction of its N-terminal domain with vesicular Rab proteins; however, the mechanisms of granuphilin plasma membrane targeting and release are less clear. Granuphilin contains two C2 domains, C2A and C2B, that interact with the plasma membrane lipid phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P2]. The goal of this study was to determine membrane-binding mechanisms, affinities, and kinetics of both granuphilin C2 domains using fluorescence spectroscopic techniques. Results indicate that both C2A and C2B bind anionic lipids in a Ca(2+)-independent manner. The C2A domain binds liposomes containing a physiological mixture of lipids including 2% PI(4,5)P2 or PI(3,4,5)P3 with high affinity (apparent K(d, PIPx) of 2-5 nM), and binds nonspecifically with moderate affinity to anionic liposomes lacking phosphatidylinositol phosphate (PIPx) lipids. The C2B domain binds with sub-micromolar affinity to liposomes containing PI(4,5)P2 but does not have a measurable affinity for background anionic lipids. Both domains can be competed away from their target lipids by the soluble PIPx analog inositol-(1,2,3,4,5,6)-hexakisphosphate (IP6), which is a positive regulator of insulin secretion. Potential roles of these interactions in the docking and release of granuphilin from the plasma membrane are discussed.
Collapse
Affiliation(s)
- Tatyana A Lyakhova
- Department of Chemistry, University of Colorado Denver, Campus Box 194, P.O. Box 173364, Denver, CO 80217, USA
| | - Jefferson D Knight
- Department of Chemistry, University of Colorado Denver, Campus Box 194, P.O. Box 173364, Denver, CO 80217, USA.
| |
Collapse
|
35
|
Moghadam PK, Jackson MB. The functional significance of synaptotagmin diversity in neuroendocrine secretion. Front Endocrinol (Lausanne) 2013; 4:124. [PMID: 24065953 PMCID: PMC3776153 DOI: 10.3389/fendo.2013.00124] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/23/2013] [Accepted: 08/31/2013] [Indexed: 11/25/2022] Open
Abstract
Synaptotagmins (syts) are abundant, evolutionarily conserved integral membrane proteins that play essential roles in regulated exocytosis in nervous and endocrine systems. There are at least 17 syt isoforms in mammals, all with tandem C-terminal C2 domains with highly variable capacities for Ca(2+) binding. Many syts play roles in neurotransmitter release or hormone secretion or both, and a growing body of work supports a role for some syts as Ca(2+) sensors of exocytosis. Work in many types of endocrine cells has documented the presence of a number of syt isoforms on dense-core vesicles containing various hormones. Syts can influence the kinetics of exocytotic fusion pores and the choice of release mode between kiss-and-run and full-fusion. Vesicles harboring different syt isoforms can preferentially undergo distinct modes of exocytosis with different forms of stimulation. The diverse properties of syt isoforms enable these proteins to shape Ca(2+) sensing in endocrine cells, thus contributing to the regulation of hormone release and the organization of complex endocrine functions.
Collapse
Affiliation(s)
| | - Meyer B. Jackson
- Department of Neuroscience, University of Wisconsin, Madison, WI, USA
- *Correspondence: Meyer B. Jackson, Department of Neuroscience, University of Wisconsin, 1300 University Avenue, Madison, WI 53706-1510, USA e-mail:
| |
Collapse
|
36
|
Yan Y, Fan W, Liu L, Yang R, Yang W. The effects of Xingnao Jieyu capsules on post-stroke depression are similar to those of fluoxetine. Neural Regen Res 2013; 8:1765-72. [PMID: 25206473 PMCID: PMC4145951 DOI: 10.3969/j.issn.1673-5374.2013.19.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2012] [Accepted: 03/22/2013] [Indexed: 11/18/2022] Open
Abstract
The Xingnao Jieyu capsule has been shown to effectively relieve neurologic impairments and lessen depression. It remains poorly understood whether this capsule can be used to treat post-stroke depression. Thus, in the present study, we established a rat model of post-stroke depression using left middle cerebral artery occlusions in combination of chronic unpredictable stress and solitary housing during development. Experimental rats received intragastric perfusion with 0.82, 0.41, and 0.20 g/kg Xingnao Jieyu capsules separately dissolved in 2 mL distilled water. Fluoxetine served as a positive control. The treatment was conducted over 28 days. Sugar water consumption test, open-field test, real-time fluorescent quantitative PCR and immunohistochemical staining results demonstrated that intragastric perfusion with various doses of Xingnao Jieyu capsules increased sugar water consumption, voluntary behaviors and synaptotagmin mRNA and protein expression in rats with post-stroke depression. These therapeutic effects were similar to those of fluoxetine. These results indicate that Xingnao Jieyu capsules upregulate synaptotagmin expression in hippocampi of rats with post-stroke depression, and exert antidepressant effects.
Collapse
Affiliation(s)
- Yongmei Yan
- Department of Encephalopathy, Affiliated Hospital of Shaanxi University of Chinese Medicine, Xianyang 712000, Shaanxi Province, China ; Encephalopathology Key Subject of Traditional Chinese Medicine, State Administration of Traditional Chinese Medicine of the People's Republic of China, Xianyang 712000, Shaanxi Province, China
| | - Wentao Fan
- Department of Encephalopathy, Affiliated Hospital of Shaanxi University of Chinese Medicine, Xianyang 712000, Shaanxi Province, China ; Encephalopathology Key Subject of Traditional Chinese Medicine, State Administration of Traditional Chinese Medicine of the People's Republic of China, Xianyang 712000, Shaanxi Province, China
| | - Li Liu
- Research Room of Traditional Chinese Medicine Internal Medicine, Shaanxi University of Chinese Medicine, Xianyang 712046, Shaanxi Province, China
| | - Ru Yang
- Department of Encephalopathy, Affiliated Hospital of Shaanxi University of Chinese Medicine, Xianyang 712000, Shaanxi Province, China
| | - Wenjia Yang
- Department of Encephalopathy, Affiliated Hospital of Shaanxi University of Chinese Medicine, Xianyang 712000, Shaanxi Province, China
| |
Collapse
|
37
|
Dean C, Dunning FM, Liu H, Bomba-Warczak E, Martens H, Bharat V, Ahmed S, Chapman ER. Axonal and dendritic synaptotagmin isoforms revealed by a pHluorin-syt functional screen. Mol Biol Cell 2012; 23:1715-27. [PMID: 22398727 PMCID: PMC3338438 DOI: 10.1091/mbc.e11-08-0707] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The synaptotagmins (syts) are a family of molecules that regulate membrane fusion. There are 17 mammalian syt isoforms, most of which are expressed in the brain. However, little is known regarding the subcellular location and function of the majority of these syts in neurons, largely due to a lack of isoform-specific antibodies. Here we generated pHluorin-syt constructs harboring a luminal domain pH sensor, which reports localization, pH of organelles to which syts are targeted, and the kinetics and sites of exocytosis and endocytosis. Of interest, only syt-1 and 2 are targeted to synaptic vesicles, whereas other isoforms selectively recycle in dendrites (syt-3 and 11), axons (syt-5, 7, 10, and 17), or both axons and dendrites (syt-4, 6, 9, and 12), where they undergo exocytosis and endocytosis with distinctive kinetics. Hence most syt isoforms localize to distinct secretory organelles in both axons and dendrites and may regulate neuropeptide/neurotrophin release to modulate neuronal function.
Collapse
Affiliation(s)
- Camin Dean
- Department of Neuroscience, Howard Hughes Medical Institute, University of Wisconsin, Madison, WI 53706, USA
| | | | | | | | | | | | | | | |
Collapse
|
38
|
Vrljic M, Strop P, Hill RC, Hansen KC, Chu S, Brunger AT. Post-translational modifications and lipid binding profile of insect cell-expressed full-length mammalian synaptotagmin 1. Biochemistry 2011; 50:9998-10012. [PMID: 21928778 PMCID: PMC3217305 DOI: 10.1021/bi200998y] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Synaptotagmin 1 (Syt1) is a Ca(2+) sensor for SNARE-mediated, Ca(2+)-triggered synaptic vesicle fusion in neurons. It is composed of luminal, transmembrane, linker, and two Ca(2+)-binding (C2) domains. Here we describe expression and purification of full-length mammalian Syt1 in insect cells along with an extensive biochemical characterization of the purified protein. The expressed and purified protein is properly folded and has increased α-helical content compared to the C2AB fragment alone. Post-translational modifications of Syt1 were analyzed by mass spectrometry, revealing the same modifications of Syt1 that were previously described for Syt1 purified from brain extract or mammalian cell lines, along with a novel modification of Syt1, tyrosine nitration. A lipid binding screen with both full-length Syt1 and the C2AB fragments of Syt1 and Syt3 isoforms revealed new Syt1-lipid interactions. These results suggest a conserved lipid binding mechanism in which Ca(2+)-independent interactions are mediated via a lysine rich region of the C2B domain while Ca(2+)-dependent interactions are mediated via the Ca(2+)-binding loops.
Collapse
Affiliation(s)
- Marija Vrljic
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, California 94305-5432, USA
| | | | | | | | | | | |
Collapse
|
39
|
Smith EA, Weisshaar JC. Docking, not fusion, as the rate-limiting step in a SNARE-driven vesicle fusion assay. Biophys J 2011; 100:2141-50. [PMID: 21539781 DOI: 10.1016/j.bpj.2011.03.015] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2010] [Revised: 03/09/2011] [Accepted: 03/14/2011] [Indexed: 10/18/2022] Open
Abstract
In vitro vesicle fusion assays that monitor lipid mixing between t-SNARE and v-SNARE vesicles in bulk solution exhibit remarkably slow fusion on the nonphysiological timescale of tens of minutes to several hours. Here, single-vesicle, fluorescence resonance energy transfer-based assays cleanly separate docking and fusion steps for individual vesicle pairs containing full-length SNAREs. Docking is extremely inefficient and is the rate-limiting step. Of importance, the docking and fusion kinetics are comparable in the two assays (one with v-SNARE vesicles tethered to a surface and the other with v-SNARE vesicles free in solution). Addition of the V(C) peptide synaptobrevin-2 (syb(57-92)) increases the docking efficiency by a factor of ∼30, but docking remains rate-limiting. In the presence of V(C) peptide, the fusion step occurs on a timescale of ∼10 s. In previous experiments involving bulk fusion assays in which the addition of synaptotagmin/Ca(2+), Munc-18, or complexin accelerated the observed lipid-mixing rate, the enhancement may have arisen from the docking step rather than the fusion step.
Collapse
Affiliation(s)
- Elizabeth A Smith
- Graduate Program in Molecular Biophysics, University of Wisconsin, Madison, Wisconsin, USA
| | | |
Collapse
|
40
|
Doi H, Yoshida K, Yasuda T, Fukuda M, Fukuda Y, Morita H, Ikeda SI, Kato R, Tsurusaki Y, Miyake N, Saitsu H, Sakai H, Miyatake S, Shiina M, Nukina N, Koyano S, Tsuji S, Kuroiwa Y, Matsumoto N. Exome sequencing reveals a homozygous SYT14 mutation in adult-onset, autosomal-recessive spinocerebellar ataxia with psychomotor retardation. Am J Hum Genet 2011; 89:320-7. [PMID: 21835308 DOI: 10.1016/j.ajhg.2011.07.012] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2011] [Revised: 07/11/2011] [Accepted: 07/15/2011] [Indexed: 01/29/2023] Open
Abstract
Autosomal-recessive cerebellar ataxias (ARCAs) are clinically and genetically heterogeneous disorders associated with diverse neurological and nonneurological features that occur before the age of 20. Currently, mutations in more than 20 genes have been identified, but approximately half of the ARCA patients remain genetically unresolved. In this report, we describe a Japanese family in which two siblings have slow progression of a type of ARCA with psychomotor retardation. Using whole-exome sequencing combined with homozygosity mapping, we identified a homozygous missense mutation in SYT14, encoding synaptotagmin XIV (SYT14). Expression analysis of the mRNA of SYT14 by a TaqMan assay confirmed that SYT14 mRNA was highly expressed in human fetal and adult brain tissue as well as in the mouse brain (especially in the cerebellum). In an in vitro overexpression system, the mutant SYT14 showed intracellular localization different from that of the wild-type. An immunohistochemical analysis clearly showed that SYT14 is specifically localized to Purkinje cells of the cerebellum in humans and mice. Synaptotagmins are associated with exocytosis of secretory vesicles (including synaptic vesicles), indicating that the alteration of the membrane-trafficking machinery by the SYT14 mutation may represent a distinct pathomechanism associated with human neurodegenerative disorders.
Collapse
Affiliation(s)
- Hiroshi Doi
- Department of Human Genetics, Graduate School of Medicine, Yokohama City University, 3-9 Fukuura, Kanazawa-ku, Yokohama, Japan
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
41
|
Mendez JA, Bourque MJ, Fasano C, Kortleven C, Trudeau LE. Somatodendritic dopamine release requires synaptotagmin 4 and 7 and the participation of voltage-gated calcium channels. J Biol Chem 2011; 286:23928-37. [PMID: 21576241 PMCID: PMC3129174 DOI: 10.1074/jbc.m111.218032] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2011] [Revised: 05/09/2011] [Indexed: 11/06/2022] Open
Abstract
Somatodendritic (STD) dopamine (DA) release is a key mechanism for the autoregulatory control of DA release in the brain. However, its molecular mechanism remains undetermined. We tested the hypothesis that differential expression of synaptotagmin (Syt) isoforms explains some of the differential properties of terminal and STD DA release. Down-regulation of the dendritically expressed Syt4 and Syt7 severely reduced STD DA release, whereas terminal release required Syt1. Moreover, we found that although mobilization of intracellular Ca(2+) stores is inefficient, Ca(2+) influx through N- and P/Q-type voltage-gated channels is critical to trigger STD DA release. Our findings provide an explanation for the differential Ca(2+) requirement of terminal and STD DA release. In addition, we propose that not all sources of intracellular Ca(2+) are equally efficient to trigger this release mechanism. Our findings have implications for a better understanding of a fundamental cell biological process mediating transcellular signaling in a system critical for diseases such as Parkinson disease.
Collapse
Affiliation(s)
- Jose Alfredo Mendez
- From the Department of Pharmacology, Groupe de Recherche sur le Système Nerveux Central, Faculty of Medicine, Université de Montréal, Montréal, Québec H3C 3J7, Canada
| | - Marie-Josée Bourque
- From the Department of Pharmacology, Groupe de Recherche sur le Système Nerveux Central, Faculty of Medicine, Université de Montréal, Montréal, Québec H3C 3J7, Canada
| | - Caroline Fasano
- From the Department of Pharmacology, Groupe de Recherche sur le Système Nerveux Central, Faculty of Medicine, Université de Montréal, Montréal, Québec H3C 3J7, Canada
| | - Christian Kortleven
- From the Department of Pharmacology, Groupe de Recherche sur le Système Nerveux Central, Faculty of Medicine, Université de Montréal, Montréal, Québec H3C 3J7, Canada
| | - Louis-Eric Trudeau
- From the Department of Pharmacology, Groupe de Recherche sur le Système Nerveux Central, Faculty of Medicine, Université de Montréal, Montréal, Québec H3C 3J7, Canada
| |
Collapse
|
42
|
Cao P, Maximov A, Südhof TC. Activity-dependent IGF-1 exocytosis is controlled by the Ca(2+)-sensor synaptotagmin-10. Cell 2011; 145:300-11. [PMID: 21496647 PMCID: PMC3102833 DOI: 10.1016/j.cell.2011.03.034] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2010] [Revised: 12/24/2010] [Accepted: 03/07/2011] [Indexed: 10/18/2022]
Abstract
Synaptotagmins Syt1, Syt2, Syt7, and Syt9 act as Ca(2+)-sensors for synaptic and neuroendocrine exocytosis, but the function of other synaptotagmins remains unknown. Here, we show that olfactory bulb neurons secrete IGF-1 by an activity-dependent pathway of exocytosis, and that Syt10 functions as the Ca(2+)-sensor that triggers IGF-1 exocytosis in these neurons. Deletion of Syt10 impaired activity-dependent IGF-1 secretion in olfactory bulb neurons, resulting in smaller neurons and an overall decrease in synapse numbers. Exogenous IGF-1 completely reversed the Syt10 knockout phenotype. Syt10 colocalized with IGF-1 in somatodendritic vesicles of olfactory bulb neurons, and Ca(2+)-binding to Syt10 caused these vesicles to undergo exocytosis, thereby secreting IGF-1. Thus, Syt10 controls a previously unrecognized pathway of Ca(2+)-dependent exocytosis that is spatially and temporally distinct from Ca(2+)-dependent synaptic vesicle exocytosis controlled by Syt1. Our findings thereby reveal that two different synaptotagmins can regulate functionally distinct Ca(2+)-dependent membrane fusion reactions in the same neuron.
Collapse
Affiliation(s)
- Peng Cao
- Department of Molecular and Cellular Physiology, and Howard Hughes Medical Institute, Stanford University, 1050 Arastradero Rd., Palo Alto, California 94305, USA
| | | | | |
Collapse
|
43
|
Zhang Z, Wu Y, Wang Z, Dunning FM, Rehfuss J, Ramanan D, Chapman ER, Jackson MB. Release mode of large and small dense-core vesicles specified by different synaptotagmin isoforms in PC12 cells. Mol Biol Cell 2011; 22:2324-36. [PMID: 21551071 PMCID: PMC3128534 DOI: 10.1091/mbc.e11-02-0159] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Different synaptotagmin isoforms (syt I, VII, and IX) sort to populations of dense-core vesicles with different sizes. These isoforms differ in their sensitivities to divalent cations and trigger different modes of exocytosis. Exocytosis triggered by these isoforms also differs in its sensitivity to inhibition by another isoform, syt IV. Many cells release multiple substances in different proportions according to the specific character of a stimulus. PC12 cells, a model neuroendocrine cell line, express multiple isoforms of the exocytotic Ca2+ sensor synaptotagmin. We show that these isoforms sort to populations of dense-core vesicles that differ in size. These synaptotagmins differ in their Ca2+ sensitivities, their preference for full fusion or kiss-and-run, and their sensitivity to inhibition by synaptotagmin IV. In PC12 cells, vesicles that harbor these different synaptotagmin isoforms can be preferentially triggered to fuse by different forms of stimulation. The mode of fusion is specified by the synaptotagmin isoform activated, and because kiss-and-run exocytosis can filter small molecules through a size-limiting fusion pore, the activation of isoforms that favor kiss-and-run will select smaller molecules over larger molecules packaged in the same vesicle. Thus synaptotagmin isoforms can provide multiple levels of control in the release of different molecules from the same cell.
Collapse
Affiliation(s)
- Zhen Zhang
- Department of Physiology, University of Wisconsin School of Medical and Public Health, Madison, WI 53706, USA
| | | | | | | | | | | | | | | |
Collapse
|
44
|
Mapping of INS promoter interactions reveals its role in long-range regulation of SYT8 transcription. Nat Struct Mol Biol 2011; 18:372-8. [PMID: 21336277 PMCID: PMC6402586 DOI: 10.1038/nsmb.1993] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2010] [Accepted: 11/30/2010] [Indexed: 02/07/2023]
Abstract
Insulin (INS) synthesis and secretion from pancreatic β cells are tightly regulated; their deregulation causes diabetes. Here we map INS-associated loci in human pancreatic islets by 4C and 3C techniques and show that the INS gene physically interacts with the SYT8 gene, located over 300 kb away. This interaction is elevated by glucose and accompanied by increases in SYT8 expression. Inactivation of the INS promoter by promoter-targeting siRNA reduces SYT8 gene expression. SYT8-INS interaction and SYT8 transcription are attenuated by CTCF depletion. Furthermore, SYT8 knockdown decreases insulin secretion in islets. These results reveal a non-redundant role for SYT8 in insulin secretion and indicate that the INS promoter acts from a distance to stimulate SYT8 transcription. This suggests a function for the INS promoter in coordinating insulin transcription and secretion through long-range regulation of SYT8 expression in human islets.
Collapse
|
45
|
Xue M, Craig TK, Shin OH, Li L, Brautigam CA, Tomchick DR, Südhof TC, Rosenmund C, Rizo J. Structural and mutational analysis of functional differentiation between synaptotagmins-1 and -7. PLoS One 2010; 5. [PMID: 20824061 PMCID: PMC2932738 DOI: 10.1371/journal.pone.0012544] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2010] [Accepted: 08/09/2010] [Indexed: 01/16/2023] Open
Abstract
Synaptotagmins are known to mediate diverse forms of Ca2+-triggered exocytosis through their C2 domains, but the principles underlying functional differentiation among them are unclear. Synaptotagmin-1 functions as a Ca2+ sensor in neurotransmitter release at central nervous system synapses, but synaptotagmin-7 does not, and yet both isoforms act as Ca2+ sensors in chromaffin cells. To shed light into this apparent paradox, we have performed rescue experiments in neurons from synaptotagmin-1 knockout mice using a chimera that contains the synaptotagmin-1 sequence with its C2B domain replaced by the synaptotagmin-7 C2B domain (Syt1/7). Rescue was not achieved either with the WT Syt1/7 chimera or with nine mutants where residues that are distinct in synaptotagmin-7 were restored to those present in synaptotagmin-1. To investigate whether these results arise because of unique conformational features of the synaptotagmin-7 C2B domain, we determined its crystal structure at 1.44 Å resolution. The synaptotagmin-7 C2B domain structure is very similar to that of the synaptotagmin-1 C2B domain and contains three Ca2+-binding sites. Two of the Ca2+-binding sites of the synaptotagmin-7 C2B domain are also present in the synaptotagmin-1 C2B domain and have analogous ligands to those determined for the latter by NMR spectroscopy, suggesting that a discrepancy observed in a crystal structure of the synaptotagmin-1 C2B domain arose from crystal contacts. Overall, our results suggest that functional differentiation in synaptotagmins arises in part from subtle sequence changes that yield dramatic functional differences.
Collapse
Affiliation(s)
- Mingshan Xue
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas, United States of America
| | - Timothy K. Craig
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Ok-Ho Shin
- Department of Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - Liyi Li
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
| | - Chad A. Brautigam
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Diana R. Tomchick
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Thomas C. Südhof
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- Department of Molecular and Cellular Physiology, Stanford University, Palo Alto, California, United States of America
- Howard Hughes Medical Institute, Stanford University, Palo Alto, California, United States of America
| | - Christian Rosenmund
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
- Neuroscience Research Center, Charite-Universitätsmedizin Berlin, Berlin, Germany
- Cluster of Excellence NeuroCure, Charite-Universitätsmedizin Berlin, Berlin, Germany
- * E-mail: (CR); (JR)
| | - Josep Rizo
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- * E-mail: (CR); (JR)
| |
Collapse
|
46
|
Wang Z, Chapman ER. Rat and Drosophila synaptotagmin 4 have opposite effects during SNARE-catalyzed membrane fusion. J Biol Chem 2010; 285:30759-66. [PMID: 20688915 PMCID: PMC2945570 DOI: 10.1074/jbc.m110.137745] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Synaptotagmins (Syt) are a large family of proteins that regulate membrane traffic in neurons and other cell types. One isoform that has received considerable attention is SYT4, with apparently contradictory reports concerning the function of this isoform in fruit flies and mice. SYT4 was reported to function as a negative regulator of neurotrophin secretion in mouse neurons and as a positive regulator of secretion of a yet to be identified growth factor from muscle cells in flies. Here, we have directly compared the biochemical and functional properties of rat and fly SYT4. We report that rat SYT4 inhibited SNARE-catalyzed membrane fusion in both the absence and presence of Ca2+. In marked contrast, fly SYT4 stimulated SNARE-mediated membrane fusion in response to Ca2+. Analysis of chimeric molecules, isolated C2 domains, and point mutants revealed that the C2B domain of the fly protein senses Ca2+ and is sufficient to stimulate fusion. Rat SYT4 was able to stimulate fusion in response to Ca2+ when the conserved Asp-to-Ser Ca2+ ligand substitution in its C2A domain was reversed. In summary, rat SYT4 serves as an inhibitory isoform, whereas fly SYT4 is a bona fide Ca2+ sensor capable of coupling Ca2+ to membrane fusion.
Collapse
Affiliation(s)
- Zhao Wang
- Department of Physiology, Howard Hughes Medical Institute, University of Wisconsin, Madison, Wisconsin 53706, USA
| | | |
Collapse
|
47
|
Zhang Z, Hui E, Chapman ER, Jackson MB. Regulation of exocytosis and fusion pores by synaptotagmin-effector interactions. Mol Biol Cell 2010; 21:2821-31. [PMID: 20573977 PMCID: PMC2921110 DOI: 10.1091/mbc.e10-04-0285] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Synaptotagmin isoforms and mutants altered fusion event frequency and fusion pore transitions. These effects showed a strong correlation with PS binding, but not with SNARE binding. Synaptotagmin-PS interaction thus function in two distinct kinetic steps in Ca2+ triggered exocytosis, and stabilize open fusion pores. Synaptotagmin (syt) serves as a Ca2+ sensor in the release of neurotransmitters and hormones. This function depends on the ability of syt to interact with other molecules. Syt binds to phosphatidylserine (PS)-containing lipid bilayers as well as to soluble N-ethylmaleimide sensitive factor receptors (SNAREs) and promotes SNARE assembly. All these interactions are regulated by Ca2+, but their specific roles in distinct kinetic steps of exocytosis are not well understood. To explore these questions we used amperometry recording from PC12 cells to investigate the kinetics of exocytosis. Syt isoforms and syt I mutants were overexpressed to perturb syt-PS and syt-SNARE interactions to varying degrees and evaluate the effects on fusion event frequency and the rates of fusion pore transitions. Syt I produced more rapid dilation of fusion pores than syt VII or syt IX, consistent with its role in synchronous synaptic release. Stronger syt-PS interactions were accompanied by a higher frequency of fusion events and more stable fusion pores. By contrast, syt-SNARE interactions and syt-induced SNARE assembly were uncorrelated with rates of exocytosis. This associates the syt-PS interaction with two distinct kinetic steps in Ca2+ triggered exocytosis and supports a role for the syt-PS interaction in stabilizing open fusion pores.
Collapse
Affiliation(s)
- Zhen Zhang
- National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892, USA
| | | | | | | |
Collapse
|
48
|
Abstract
Synaptotagmins (Syts) are transmembrane proteins involved in the regulation of membrane trafficking. Here, we summarize literature data that provide growing evidence that several Syts are involved in the pathophysiological mechanisms of temporal lobe epilepsy and Parkinson's disease, as well as few reports related to brain ischemia and Alzheimer's disease (AD). We also report new data from our laboratories, showing changes of the expression of several Syts in Tg2576 mouse model of AD that may be related to neuroinflammation surrounding the beta-amyloid plaques. Furthermore, we demonstrate N-methyl-D-aspartate receptor-mediated upregulation of Syt 4 mRNA in a model of excitotoxic striatal lesion induced by unilateral striatal injection of quinolinic acid, associating the upregulation of Syt 4 with mechanisms of excitotoxicity. We propose that pharmacological manipulation of Syt expression in animal models of neurodegeneration should be further explored, as it may help to clarify the role of individual Syt isoforms in the regulation of membrane trafficking in neurodegeneration.
Collapse
Affiliation(s)
- Gordana Glavan
- Medical Faculty, Institute of Pathophysiology, University of Ljubljana, Ljubljana, Slovenia
| | | | | |
Collapse
|
49
|
Molecular mechanism of the synaptotagmin-SNARE interaction in Ca2+-triggered vesicle fusion. Nat Struct Mol Biol 2010; 17:325-31. [PMID: 20173762 PMCID: PMC2928146 DOI: 10.1038/nsmb.1764] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2009] [Accepted: 12/11/2009] [Indexed: 12/15/2022]
Abstract
In neurons, SNAREs, synaptotagmin, and other factors catalyze Ca2+-triggered fusion of vesicles with the plasma membrane. The molecular mechanism of this process remains an enigma, especially regarding the interaction between synaptotagmin and SNAREs. Here we characterized this interaction by single-molecule fluorescence microscopy and crystallography. The two rigid Ca2+-binding domains of synaptotagmin 3 undergo large relative motions in solution. Interaction with SNARE complex amplifies a particular state of the two domains that is further enhanced by Ca2+. This state is represented by the first SNARE-induced Ca2+-bound crystal structure of a synaptotagmin fragment containing both domains. The arrangement of the Ca2+-binding loops of this structure of synaptotagmin 3 matches that of SNARE-bound synaptotagmin 1, suggesting a conserved feature of synaptotagmins. The loops resemble the membrane-interacting loops of certain viral fusion proteins in the postfusion state, suggesting unexpected similarities between both fusion systems.
Collapse
|
50
|
Craxton M. A manual collection of Syt, Esyt, Rph3a, Rph3al, Doc2, and Dblc2 genes from 46 metazoan genomes--an open access resource for neuroscience and evolutionary biology. BMC Genomics 2010; 11:37. [PMID: 20078875 PMCID: PMC2823689 DOI: 10.1186/1471-2164-11-37] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2009] [Accepted: 01/15/2010] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND Synaptotagmin proteins were first identified in nervous tissue, residing in synaptic vesicles. Synaptotagmins were subsequently found to form a large family, some members of which play important roles in calcium triggered exocytic events. These members have been investigated intensively, but other family members are not well understood, making it difficult to grasp the meaning of family membership in functional terms. Further difficulty arises as families are defined quite legitimately in different ways: by common descent or by common possession of distinguishing features. One definition does not necessarily imply the other. The evolutionary range of genome sequences now available, can shed more light on synaptotagmin gene phylogeny and clarify family relationships. The aim of compiling this open access collection of synaptotagmin and synaptotagmin-like sequences, is that its use may lead to greater understanding of the biological function of these proteins in an evolutionary context. RESULTS 46 metazoan genomes were examined and their complement of Syt, Esyt, Rph3a, Rph3al, Doc2 and Dblc2 genes identified. All of the sequences were compared, named, then examined in detail. Esyt genes were formerly named Fam62. The species in this collection are Trichoplax, Nematostella, Capitella, Helobdella, Lottia, Ciona, Strongylocentrotus, Branchiostoma, Ixodes, Daphnia, Acyrthosiphon, Tribolium, Nasonia, Apis, Anopheles, Drosophila, Caenorhabditis, Takifugu, Tetraodon, Gasterosteus, Oryzias, Danio, Xenopus, Anolis, Gallus, Taeniopygia,Ornithorhynchus, Monodelphis, Mus and Homo. All of the data described in this paper is available as additional files. CONCLUSIONS Only a subset of synaptotagmin proteins appear able to function as calcium triggers. Syt1, Syt7 and Syt9 are ancient conserved synaptotagmins of this type. Some animals carry extensive repertoires of synaptotagmin genes. Other animals of no less complexity, carry only a small repertoire. Current understanding does not explain why this is so. The biological roles of many synaptotagmins remain to be understood. This collection of genes offers prospects for fruitful speculation about the functional roles of the synaptotagmin repertoires of different animals and includes a great range of biological complexity. With reference to this gene collection, functional relationships among Syt, Esyt, Rph3a, Rph3al, Doc2 and Dblc2 genes, which encode similar proteins, can better be assessed in future.
Collapse
Affiliation(s)
- Molly Craxton
- Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge CB20QH, UK.
| |
Collapse
|